Impossible to fix flow problem? 4 grand down so far...

[Old UKPF 99429]

Hi,

Was hoping to get some advice... When I moved in the central heating was not working (they didn't tell us), paid quite a bit of cash to get it looked at, everything pointed at flow problems as the "Ideal" boiler would display flow error code. In the end, the plumber let me down, so went with another plumber and decided to install brand new boiler, a Viessmann Vitodens 100-w.

Basically, 2 years on, still having the same problems. It was open vented, but has been converted to sealed system, doesn't lose pressure. Had new pumps (currently got Grundfos Alpha2L 15-60 (130)), and still not getting any heat into the rads. We have 12 rads, 3 large ones, all doubles. Most have TRVs.

The boiler starts up, shoots up to 50 degrees quite quickly and cuts out, then repeats. Oddly it does this even on hot water, a much much shorter circuit. Eventually the hot water does heat up a little bit. Today I started it up to see if it was working (as it was sort of "working" over the winter, but badly), and it just short cycles as above, no heat into any rads after 45 mins of running. The heat/burner display has never ever been above 1 (out of 4 or 5 levels).

It has been power flushed (although not sure how well), and various other bits of work and has eaten a ton of money. have tried balancing but something more fundamental is wrong I thing, or this boiler is just terrible. Also, doesn't seem to be air in the system as it is sealed now, and never any air in rads at all, immediate water trickles out (very clear water).

I am a bit desperate now as I honestly don't know what to do next, can't keep throwing money at it... Any advice really is much appreciated. Hoping someone might be able to help.

 

[ShaunCorbs]

Sounds like you need a engy to look over the system could be a pump or a blockage as it sounds like its not circulating

 

[Karl]

Really sounds as if the system is badly blocked, or something stupid like an isolator out of view turned off maybe. If it was me I would take a radiator off make sure all other rads are isolated put a hose on radiator pipe and see if you get flow when filling system (as long as filling loop is on boiler) test both pipes on radiator this way, if no luck try on a couple other radiators at opposite ends of system. If pipes are that badly blocked then it might be cheaper to replace pipe work and is it any chance micro-bore pipes? Can’t believe someone has fitted you a new boiler and walked away without the system working!

 

[AMGasServices]

Do your flow and return pipes get warm under the boiler ?

How far can you trace these pipes ? Check if they’re heating up.

Do you have a hot water tank in the house ? If so Please post pictures of this.

 

[rpm]

Microbore pipe anyone?

 

[Old UKPF 99429]

Hi all, no microbore in the system. It does have a hot water tank (will try and grab some pics tomorrow). The ground floor pipes are mostly under screed. There are three returns, hot water, upstairs and downstairs rads. The system has been working, and have had heat into all radiators, but always been slow and rubbish. The more rads I turn off, the better the boiler performs (as in, it cuts out less).

When it was powerflushed (with the boiler on) heat got into every rad within seconds. And when the hot water turns on for the first time, the boiler heats up for a bit, heat comes in to the return, and yet the boiler still cuts out!

I have never ever had a "hot" return pipe coming up from the floor (the downstairs return), the hot water return has been hot, and the upstairs return has been hot too. But at the moment it just cuts out and heat never gets into the return. Flow gets hot while heating, then quickly goes cold when cut-out.

 

[Old UKPF 99429]

All three return pipes meet in the boiler cupboard near the boiler. Boiler is downstairs in garage, pump is upstairs in airing cupboard. Pump is on full, anything less and the system is even worse.

Was wondering if it is possible to put a secondary pump on the return. Or if there is any clever way to actually determine if there really is a flow problem, like flow meters strategically placed??

 

[rpm]

Microbore pipe anyone?

Well that didn't help so would a thermo camera help?

 

[chris watkins]

There are flow meters available, Caleffi do a good one.
It does sound like you may benefit from hydraulic separation of the boiler & the system but a good heating man would need to have a look at the system layout as these 3 returns don't sound quite right
Balancing valve with flow meter

 

[chris watkins]

Nothing wrong with the Viessmann Vitodens, well at least there wasn't until someone was power flushing through it. 😕

 

[townfanjon]

You need to check if there is a temp difference back at the boiler before spending anymore money .

 

[chris watkins]

Just a thought but when the system was converted to a sealed one was the old pipework around the tee's to the open vent / cold feed removed or were they left in & capped / adapted?
It sounds like there is a large restriction somewhere & power flushing does not always clear them.

 

[Best]

I had one job that had similar problem which I eventually discovered had a seized motorised valve below a floor.
Not saying that is possible on this occasion, but just putting out that point.

 

[Old UKPF 99429]

Thanks for taking the time to reply. When converted to sealed, the old stuff was removed (F/E tank) and capped off.

Does it not sound normal to have 3 returns converging at the boiler, one comes up out of the screed, and two from upstairs. One other thing the return on most of the radiators (or all) is always cold. So def is a problem with return. But none of it makes sense when you add all the symptoms together.

It's hard to comment on the temperature difference between flow and return at the boiler as it doesn't stay on long enough to get good heat into the system, but when it has been working the flow is always hot, return lukewarm to warm (after hours of running). The boiler always "kettles" on starting up too.

Everything keeps telling me it needs a bigger pump, or secondary pump on the return, or possible another more thorough powerflush (or a powderflush?!). Don't mind spending a bit more on it, but just have no idea what should be the next move.

 

[Harvest Fields]

Thanks for taking the time to reply. When converted to sealed, the old stuff was removed (F/E tank) and capped off.

Does it not sound normal to have 3 returns converging at the boiler, one comes up out of the screed, and two from upstairs. One other thing the return on most of the radiators (or all) is always cold. So def is a problem with return. But none of it makes sense when you add all the symptoms together.

It's hard to comment on the temperature difference between flow and return at the boiler as it doesn't stay on long enough to get good heat into the system, but when it has been working the flow is always hot, return lukewarm to warm (after hours of running). The boiler always "kettles" on starting up too.

Everything keeps telling me it needs a bigger pump, or secondary pump on the return, or possible another more thorough powerflush (or a powderflush?!). Don't mind spending a bit more on it, but just have no idea what should be the next move.

I would Scrap the old flow and return and start again.

 

[Old UKPF 99429]

As in, get them fully re-piped? I guess I would have to get the whole downstairs re-piped as it is all under screed.

 

[chris watkins]

Darryl the problem isn't the return it is the circulation around the circuit/s i.e. flow rate (amount of water going past the boiler to carry the heat away)
Putting another pump on the system is not going to be the answer either, all that will do is increase the push but not the flow rate.
If the first power flush didn't work why do you think anther one will?

From the posts so far you should understand that there is no simple fix, without being able to see the system layout we can't take this any further.
A 12 rad system is not that large & the 15/60 should be able to deliver the required flow rate to this.
With all the rads turned off (and the heating zone valves shut) dose the heat flow between the boiler & the hot water cylinder above? if not then you need to get a heating engineer in.
Where are you based perhaps someone on here could help?

 

[Old UKPF 99429]

Understood, and thanks for the advice. I know they replaced all ras with doubles, so wanted to check the pump was man enough for 9 doubles, 3 of which are huge 2m ones. Sounds like it should be.

Maybe time for a full re-pipe!!

 

[sammathias]

They replaced all the rads and powerflushed...sounds like a blockage or valve/pump fault

 

[Harvest Fields]

Are both valve on each radiator fully open?

 

[Old UKPF 99429]

They are not all fully open, although yesterday went round and opened most up. It the past it behaved better with some turned off completely, and with them balanced a bit.

 

[Harvest Fields]

Remember the position of them all by writing them down then open them all fully. Then close them all apart from one and see if that one gets hot all the way back to the boiler then close that one and open another until you get to the last rad

 

[Old UKPF 99429]

Thanks, will do that. I always read start with the one closest to the boiler, but think I need to start with one close to the pump (which is upstairs)? Never know which is first in line. But will shut them all off tonight and try. What would it tell me if it works fine with just one radiator! (which I think it might)...

 

[Harvest Fields]

Thanks, will do that. I always read start with the one closest to the boiler, but think I need to start with one close to the pump (which is upstairs)? Never know which is first in line. But will shut them all off tonight and try. What would it tell me if it works fine with just one radiator! (which I think it might).

Not a lot you need to do each rad one at a time

 

[Best]

You have very slow flow in the circuits and that is why balancing and turning some rads was appearing to help the system work better.
It could be a part blockage or a valve somewhere nearly closed.
It can be in the flow or return and the return being cool proves nothing.
Have any of the tee off connections on the return where old cylinder etc was checked for blockages. A strong magnet out against a copper fitting or pipe will suggest magnetite at that point if the magnet is pulled to the pipe/fitting.

 

[Old UKPF 99429]

Phoned Viessman today and they were adamant that is was a circulation problem (as am I). They even finished my sentence for me, I said "my boiler starts up, the temp increases... " and he said, "and then cuts-out at 50 degress, and goes back down again"... Apparently because it is looking for a temperature difference of 20 degrees between flow and return (as expected).

Best - I had thought that perhaps it could be some of the old piping right next to the boiler where the 3 returns join together, might explain why probalem seems to occur on HW only, HW and DH, and just CH?! Even though they are separate returns...

 

[sammathias]

Send us some pictures of this pipework fella.

 

[Rob Foster]

I like this type of problem, where are U based

 

[ShaunCorbs]

I like this type of problem, where are U based

about 80 miles between you and the op

 

[fixitflav]

Does it not sound normal to have 3 returns converging at the boiler, one comes up out of the screed, and two from upstairs.

There's nothing wrong with that, I've lived in houses with that arrangement. The only thing you need to watch is that all heating returns must be commoned before the HW return comes in, or you can get flow through rads when HW only calling. But it wouldn't cause your symptoms.
For your problem, do you have a 3-port valve or 2 (or more 2-ports)? If the latter, worth making sure none is stuck closed. Though if it's wired correctly the boiler and pump should run only when 1 or more is open, to avoided dead-heading.
Is there a bypass in the system? If that is wide open it might be taking all the flow, with little or none left for the rads.

 

[Rob Foster]

about 80 miles between you and the op

160 miles No bother thats about 2.5 gall of diesel in my stink pot 4 round trip, msg me and I will come and see what can be done.

 

[Old UKPF 99429]

Got a three port valve, that is also new (well, 20 months old and seems to be working fine), it sits 2 inches above the pump. No idea if I have a bypass valve? Sorry, wouldn't know where to look?!

I turned all rads off apart from one earlier, and still no joy. The boiler simply shoots up to 50 then cuts-out, the rad does get a little heat into and would get hot if the boiler would stay on. Also, then turned on a towel rad, same story, rad immediately got warm, but never hot as the boiler wouldn't stay heating... So clearly, the circulation is not good, although the boiler is looking for 20 deg differential between flow and return rather than measuring flow rate I think.

So, it was sort of working, with around 8 rad (some turned off) at the end of winter, slow to heat, but would heat up eventually. And yet now, after being left for 4 months, doesn;t work at all. Not sure what that tells me!

 

[sammathias]

Don't the vitodens have an internal pump and you also have an external pump? Bypass would be fitted after pump before 3 port valve. Need some pictures of your set up...boiler pipework/ pumps etc.

 

[Jim Goodenough]

Have you checked pump valves are both fully open. Very basic suggestion but could be a knackered pump valve??

 

[fixitflav]

No idea if I have a bypass valve? Sorry, wouldn't know where to look?!

The bypass (if there is one) would be from pump discharge to boiler return, in parallel with the load, so if the rad controls throttle down to nothing there is still a flow through the boiler. I believe modern bypass valves don't just throttle but have some flow control feature, so they don't bypass a lot of flow when not necessary.

the boiler is looking for 20 deg differential between flow and return rather than measuring flow rate I think.

I don't understand that, perhaps the experts here can explain. For a given pump flow and boiler design output, the differential is fixed. If that is greater than 20°C, and the boiler is looking for a maximum 20° differential, when that is reached I would expect it to modulate (on a modern boiler) to maintain 20°, but then boiler output is below design. To get design output, need to increase the water flow. As the system heats up, if it's working properly the flow and return temperatures both rise, keeping the 20° differential.
But I don't see any advantage over controlling to a boiler flow (output) temperature, the more traditional way.
There doesn't seem any reason to think your water flow is blocked, and it would have to be severe to give your symptoms, so it looks to me like a boiler control issue. Might be worth discussing with Viessmann, and asking if there are any other options for boiler control.

 

[sammathias]

The boiler always "kettles" on starting up too.

Boiler empty 😎

 

[Old UKPF 99429]

Fixitflav - and that is what I don't get... Seems to me like perhaps I do have a circulation problem a bit but def no blockage as such. And it feels like the boiler is just too picky about the conditions it will operate in. Thinking the only way to tell for sure is putting a flow sensor in, on the return by the boiler? Could just be that I have some circulation, but very limited, the pipes are 35 years old...

 

[Old UKPF 99429]

I also think if I was to put a huge pump in there, it might just work!

 

[fixitflav]

Fixitflav - and that is what I don't get... Seems to me like perhaps I do have a circulation problem a bit but def no blockage as such. And it feels like the boiler is just too picky about the conditions it will operate in. Thinking the only way to tell for sure is putting a flow sensor in, on the return by the boiler? Could just be that I have some circulation, but very limited, the pipes are 35 years old...

Maybe sammathias has a point, it could be as simple as that. What is system pressure? Is there flow from a vent point on the boiler, or the pipework close by?
Where is the expansion vessel connected?
Some photos and sketches would be useful.

 

[Old UKPF 99429]

System pressure is sat around 0.6 bar rising up a bit when hot water is on currently. Can top it up later, didn't think that would make a huge difference? Expansion vessel is connected on the return I think, next to the boiler, will draw it out later... Wasn't sure I understood the question about flow from the vent point on the boiler?

 

[Harvest Fields]

Pressure should be between 1 and 1.5 dependant on boiler when cold

 

[Old UKPF 99429]

I am thinking the only way to bottom this out is to buy some flow meters and determine once and for all if I have flow or note? One was suggested in earlier post, but also found these Piusi K24 AdBlue™ Flow Meter | BEST Price | In Stock | Fast Del|

 

[sammathias]

A small grundfos 15/50 will be capable of heating a 12 rad system...what makes you think a huge pump is going to make any difference? Going down the route of flow meters is just wasting time and money.
Time to get a decent heating engineer out and get him to read the installation instructions on bleeding the boiler to start. And look over your heating system. No doubt something straight forward.

 

[fixitflav]

Wasn't sure I understood the question about flow from the vent point on the boiler?

The system should have a number of manual air vent points, usually just a knurled nut to open. The one near the boiler will give some idea whether the boiler is full. Water should flow from the vent.

 

[chris watkins]

Darryl why do you think you are still capable of sorting this out & why no photos ?
If the boiler does the same thing when just the hot water is on (no heating) a small 22mm flow & return, then the problem lies on the primary circuit between the boiler & the upstairs cylinder cupboard. A flow meter is going to tell you what we already know & then what, what will you do to fix it?
Find someone who understands what they are doing, it is more than likely a simple fix as a number have suggested.
I am out of here, good luck.

 

[Old UKPF 99429]

Thanks. I don't think I am capable of fixing it, I know I am not, just looking for some creative ideas and to learn a little really. Had two different plumbers out so far, 4k spent and the system is behaving identically, they tried all the "simple fixes" apparently and some more complex ones. Really appreciated the responses and ideas.

Tried to take some pics last night and all the useful bits are blocked by the big red pressure ball thing from the sealed system! Will try again or draw it down later.

 

[Harvest Fields]

Thanks. I don't think I am capable of fixing it, I know I am not, just looking for some creative ideas and to learn a little really. Had two different plumbers out so far, 4k spent and the system is behaving identically, they tried all the "simple fixes" apparently and some more complex ones. Really appreciated the responses and ideas.

Tried to take some pics last night and all the useful bits are blocked by the big red pressure ball thing from the sealed system! Will try again or draw it down later.

There’s your problem. You need a heating engineer and not a plumber mate.

 

[Old UKPF 99429]

Valid point...

 

[Old UKPF 99429]

 

[sammathias]

Oooosshh. How many copper pipes do you have coming from the boiler itself?

 

[Harvest Fields]

Oooosshh. How many copper pipes do you have coming from the boiler itself?

Good question.

 

[sammathias]

Picture of under the boiler at connections?

 

[Gasmk1]

no bypass ?

 

[sammathias]

no bypass ?

I think that's the least of his worries.

 

[Gasmk1]

i know it looks like a shocker of an install

 

[Karl]

Ask around friends, family or even the local plumbers merchants for a highly recommended heating engineer! Word of mouth and reputation is the best advertisement
Good luck

 

[AMGasServices]

Is it me or are the flow and return pipes looped together ? (if you look at the second picture on the second row)

 

[chris watkins]

I know I said I would come back but
if you paid £4k for that you were quite royally tucked up mate. 22mm equal tee before the pump what is that for ?
York, E/F & compression used, there are 2no. 22mm couplings on a 150mm length in-between a tee & elbow, more like wiped joints than soldered, get a pro in & stop messing around.

 

[AMGasServices]

I agree with Chris.

Personally I’d rip up the piping the cylinder cupboard and around the boiler and repipe the lot.

 

[Old UKPF 99429]

Pictures might be a bit confusing. Connections are at the top of the boiler, just 2, 1 flow, 1 return. They are not looped together but the pic makes it look like it. 3 pipes into the roof. Flow going up, and two returns from upstairs. H/w return and upstairs rads. They join the pipe from the flood on the far right, downstairs return...

 

[Old UKPF 99429]

Some of that pipework in the boiler cupboard a crap DIY job previous owner must have done to pipe in a shower pump. Not linked to heating circuit.

 

[AMGasServices]

I have uploaded a image how your systems should look but it is not 100% correct as there are a few things missing.

 

[Old UKPF 99429]

Thanks. So even so some of the pipe work is a bit shoddy right. There seems to be nothing fundamentally wrong. Flow up to pump, into auto valve and feeding dhw tank and/or rads. H/w and rads returns all into boiler cupboard. Pressure tank on return in boiler cupboard with filling loop...

 

[Old UKPF 99429]

Expansion vessel, not pressure tank! Couldn't remember the words.

 

[sammathias]

22mm equal tee before the pump what is that for ?

Looks like the old feed and vent, can only assume it's capped off higher up and not just isolated on that 15mm gate valve.

The flow and return does loop together by some form of close coupled tee arrangement.

If your certain that that motorized valve is working correctly and the wiring is correct it probably is a blockage 'solder' .

In picture 5 you could unjoin the two 22mm tees far right and see how it performs.

Basically with that complete mess it's going to be impossible for us and best to get a 'plumber' to rectify that pipework.

 

[Rob Foster]

It might be an idea to fit a second hand pump on the rtn, wire it straight to a plug, plug it in let it run all the time on fast and see what happens. 2nd hand pump is dead cheap

 

[Old UKPF 99429]

I have two spare second hand pumps! I wondered if that would be ok to try that?

 

[sammathias]

I disagree.

 

[Darren Jackson]

Which way is the arrow pointing on the pump body? Hard to see on your picture. Also if the boiler was connected when flushed it could be full of crap now. Might be worth cleaning out the hex, plate & F/R valves.

 

[sammathias]

Darryl I will ask again but reword it. How many connections/tappings/valves are there on the underside of the boiler?

 

[Old UKPF 99429]

Thanks again for taking time to respond. Got Viessmann coming out today to check the boiler.

Will check the pump arrow direction, and will confirm if there are any pipes and connections at the bottom of the boiler from memory just one, plastic pipe?

 

[sammathias]

Ohh hopefully they don't condemn that boiler then. Let us know how you get on and weather they resolve the problem.

 

[fixitflav]

connections at the bottom of the boiler from memory just one, plastic pipe?

That's probably to be the condensate drain.

Consensus is it's likely to be low or no flow causing the problem. Re-reading your original post, I would guess the system has never worked, and the old boiler would have been fine if the flow issue had been sorted.
Assuming it is low flow, it could be due to a blockage or maybe the way the piping is installed. A sketch of the complete system would be useful, but not easy to prepare as much of the pipework will be out of sight. On a working system you can get some idea by following rising temperature round the system, but that's catch-22 in your situation.
Keep us posted about how you get on with Viessmann.

 

[Old UKPF 99429]

So, Viessmann came and went. He was adamant (obviously) that it was a flow problem! In his opinion, it is a blockage in the heat exchanger. This is because it does indeed behave exactly the same on just HW as CH. Possibly caused by powerflushing the system with the new boiler connected (as was mentioned), so has flushed some gunk down in to the heat exchanger.

His suggestion, get the boiler powerflushed, or just heat exchanger removed and cleaned fully. Put a magnaclean or some kind of filter on the return...

 

[Old UKPF 99429]

He only determined it by measuring flow and return temps. But was sure.

 

[Rob Foster]

so no result thats boring and AUTUMN is approaching. You will have to get someone in and maybe pay. See what the collective wisdom here says again. And then who ? cause you have done that ! hmmm

 

[Rob Foster]

I was again going to offer to look 'at cost' if you are not too far away cost wise and give you a contact no but your settings are precluding this -

 

[Old UKPF 99429]

Not shy of paying if that is what the implication is? Already had two plumbers/heating engineers out, approx 8 visits, maybe 4 days of work. Cost of 3.5k to 4k so far (900 initial investigations, new 3 port valve, air release valve, more diagnostics, 2.2k on new boiler and installation, further 900 ish on conversion to sealed system, new pump fitted, another new pump (bigger)) etc. etc. etc....

It's been "broken" for two years, hence I thought I would see if people had any ideas, just might have unearthed something. And it is clear it is a flow problem, needs a heating engineer to come and look again. Darn it.

 

[sammathias]

You had 2 plumbers out, one being the one who installed boiler...then you payed £900 to seal the system which judging by the pictures would have cost next to nothing for materials. I cant see how you have had so many incompetent people to look at it. Things just don't add up. I'm starting to think it's not even a legal install. Did the veissmann engineer not even bat an eyelid over the shoddy pipework/installation?

 

[fixitflav]

His suggestion, get the boiler powerflushed, or just heat exchanger removed and cleaned fully.

Sounds like the original powerflush was done after the new boiler was installed, if it's suspected that the powerflush drove muck into the h/ex. But I'm still puzzled why the flow was low enough to give those symptoms with the original boiler. I don't think we can rule out yet the blockage being elsewhere in the system.
Also if powerflushing is going to shift it, I wonder why on the original powerflush the muck wasn't swept through the h/ex and discharged.
I had a similar problem a few years back after powerflushing, I didn't know at the time not to powerflush through the boiler. We live and learn! No obvious flow problem, but very noisy (there were other issues which didn't help - gas pressure too high, and pump output down due to clogged impeller). I cured it by chemical cleaning, just through the boiler and HW cylinder, to make sure the boiler got the full benefit.

 

[Rob Foster]

I am finished with this one - it going around in circles the OP has had loads of help and assistance. I hope he gets it sorted I will just watch now

 

[Old UKPF 99429]

Thanks again all, really useful info and advice, and asnwered lots of questions on bits I had no clue about. Will def post back if I ever get it fixed!! Going to try a boiler powerflush (as mentioned just on HW circuit only), and get that booked in first, and possibly a full powerflush. I agree Flexitflav, the symptoms and history of problems with flow still doesn't quite fully add up together.

 

[Jim Goodenough]

Darryl, did you read my earlier post?

Have you checked pump valves are both fully open. Very basic suggestion but could be a knackered pump valve??

Just you may have missed it as there's been a lot of comments/suggestions.

 

[Old UKPF 99429]

Thanks Jim, will check that.

 

[Murdoch]

I think the £4K is BS and the OP is trying to do it all himself ..... the pipework is not of a time served plumber, that's for sure

Just saying what most people are thinking

 

[Old UKPF 99429]

Good one.

 

[Old UKPF 99429]

Already listed the costs, was just after some advice from some kind people. Gratefully received. Let's leave this here. Thanks again everyone for the things to try etc.

For the record I can't do any plumbing myself and wouldn't try.

 

[fixitflav]

Already listed the costs, was just after some advice from some kind people. Gratefully received. Let's leave this here. Thanks again everyone for the things to try etc.

For the record I can't do any plumbing myself and wouldn't try.

Thinking about this again, it seems odd that everything heated up during powerflush (your #6) but not otherwise. I suppose a powerflush pump has more umph than a heating pump, but still strange. Is it possible there's a spring-loaded valve somewhere in the system?

 

[oilmark]

Probably debris in the flow/return pipes unable to be power flush cleared. I bet its chipboard from a lid on the old header tank. Any evidence of chipboard particles near disused header?

 

[DerekJB]

Hi is it possible you have a check valve on the system somewhere? Have found these hidden in a few places, and I would Powerflush every individual loop and see what happens, you could put a cleaning solution in the system and run for a week then flush it. Fit an primary filter on the return first though or all the crap will go in the heat exchanger.

 

[Viper Gas]

Check direction of your rad valves and make sure flow is concurrent.

 

[Trotter31]

I noticed 2 gate valves in your photos.
Have you checked that BOTH open and close properly?
Just a thought!

 

[Bibbs118]

Bypass could be open.

The return from the cylinder should be the return nearest the boiler.

 

[sammathias]

Clutching at straws!

 

[kris]

If it was me id drain system ' remove gate valves make sure there fully open, if there ok id check zone valves and automatic bypass . If everything seems ok id disconnect flow and return near boiler and blast a compressor down ( shutting every rad apart from 1 and at one by now check airflow going round the flow and return . The fact it had a powerfully should be adequate but was it a machine or someone just pouring in chemicals ) there has to be a simple explanation even if tricky to find but a good engineer will find with out costing thousands .

 

[kris]

Just had a look at the pics of your system and tbh looks very diy ish and unprofessional. Don't take offence but there's a good chance it's simply the way it's piped that's causing issues .

 

[Harvest Fields]

If it were me, like I said before I would put a complete new flow and return in.

 

[doitmyself]

the circulation is not good, although the boiler is looking for 20 deg differential between flow and return rather than measuring flow rate I think.

I don't understand that

It appears that the Viessmann "expert" doesn't understand either.

The installation manual explains it like this:

Flow rate monitoring
Flow switch
The boiler is equipped with a flow switch for monitoring the minimum flow rate. The burner is shut down at a heating water flow rate below 200 l/h. No fault message is shown.
Recording the differential between the boiler water temperature and return temperature
The flow rate through the boiler is monitored by recording the differential between the boiler water temperature and the return temperature. Monitoring of the temperature spread with the boiler water temperature sensor and the return temperature sensor is an additional safety mechanism.
■ At a differential of > 25 K/< 30 K, the burner is operated at the lower heating output.
■ At a differential of > 30 K, the burner is switched off.
In such cases, check whether the heating system is adequately vented and the circulation pump is pumping sufficient
heating water.

200 litre/hr is equivalent to a differential of 35C at minimum output of 7.9kW.

 

[sammathias]

There was not veissmann engineer I'd say.

 

[Everal]

I would Scrap the old flow and return and start again.

SOUND