Advice needed. Issues with underfloor heating and hot water system for new build

[Carrera]

Hi, i am looking for advice regarding my system. The plumber/heating engineers have been going round in circles trying different things and I am not sure they're will get to a solution.

The issues -
1. When the underfloor heating is on, the hot water cylinder does not heat up.
2. When heating just the hot water cylinder, the boiler starts cycling heavily.
3. Underfloor heating individual loops, flow rates drop as more manifolds come online.

The system -
Worcester Bosch 40cdi conventional, grundfos Magna 1 pump, Ariston 500 litre hot water cylinder, all located in a basement plant room. There are 6 underfloor heating manifolds, with ports varying from 6 to 10 with differing loop lengths, arranged over 4 floors. The system is controlled via a heatmiser network system with 30 stats in each room. There is also a towel radiator curcuit with 6 rads which we have not yet bought into the combined running equation yet.

The flow out of the boiler goes to the pump, then up to the two feeds to the manifolds ( First feed to 3 manifolds on one side of the house, ground floor, first floor and attic floor, second feed to 2 other manifolds ground floor and first floor and a third feed to the towel rad circuit). Before these feeds there is a T which feeds the hot water cylinder and the final manifold in the basement.

Temperatures at the manifolds in consistent at about 42c and the holier is outputting at 71c.

All zone valves operate correctly, all stats and timers are running and wired correctly.

Heat loss calcis have been done to size the boiler to the heat output required, indicating the boiler is oversized by about 8kw. The system has been in for about a year and it took us a while to figure out why the water was not heating properly.

Effectively when the heating is on the flow does not go through the T to the cylinder, but when the heating is off it does and therefore heats up the water.

Things that have been tried - pump has been upgraded to the one now in place, pipe work taken apart an equivalent of a low loss header using loops and spaced Ts has been tried and then removed. The T has been turned around to reduce resistance.

Any help or advice would be really appreciated as this is driving me nuts.
If I have missed vital information please let me know and I will try and answer.
many thanks in advance.

 

[Nostrum]

I take that back as I have read the O.P wrong...

 

[Nostrum]

So when the heating only is running carrera, is the heating working effectively?

You haven't mentioned any problems with it, just the hot water?

 

[Nostrum]

Manifold temp is a constant 41 degrees, is that what it is set to?

 

[solutions]

View attachment 16396
Don it albeit sideways!
this is the plant room setup

 

[Ermintrude]

Build a nice LLH and set pumps up for ufh with a pipe stat on return to manifolds (floor side) controlling pumps on and off. I always build in a two port on flow but that's down to you.
Towel Warner's on own pump with prog stat.
DHW on its own with a two port and a balancing valve

I would in hindsight install balancing valves and a Venturi plate on each return to allow the system to be balanced properly as currently the washing up in a student house if 8 lads looks easier to balance .

LLH should have a decent internal volume to buffer the system or install an thermal store which with a few take offs and this will act as your LLH. ACV do one. But that's about £2k.

The ACV SLME is the jobbie.

 

[chris watkins]

My two pennies worth - As I understand it (& I have only skimmed read through post) hot water on it's own works & heating on it's own works ? So why not just set time clock to allow heating of cylinder before U/F heating is allowed to come on if timed or if on continuously then at times least likely to effect heating?? If this works then fine for the moment (could also think about installing diverter valve with HW priority)
The long & short is that boiler / pipework can't supply both simultaneously as installed so if you want / need a long term solution then it's going to require what the boys are suggesting.
P.S. What is the third timed zone on the Horstmann, towel rails ?

 

[diamondgas]

If there is an undersizing issue then you could maybe consider installing a separate boiler for the water alone? That may work out cheaper than rejigging, IF that's required? I'd still like to know what circulating temps you're getting with different scenarios. I've seen extremely large houses run on a 15mm one-pipe system work no problem ... but heyho! Not at the property so I'm not experiencing what the installer is! You could even potentially have an issue with the new appliance that's starving the installation of heat? I could throw a few more 'possibilities' in the pot, none would be of benefit to be honest! Striping it back to basics you need to know (A) that there's enough heat being produced; you can then look at circulation and balance if you have (A)... If you haven't got (A) then there's a possibility that when the heating comes on it 'sucks' the heat out of the cylinder, the coil in effect works in reverse as colder primaries draw heat FROM the cylinder resulting in colder hot water .... Monitoring primary F&R temperatures can tell you a great deal about how well the demands are being met ....IMHO 🙂

 

[Centralheatking]

Looks to me like Diamond gas has got it right - its a nice set up but underpowered
just go get another boiler and hook it in as suggested CHK

Its been a great post 10 pages and 35 likes and we all have
learned from it thank you CHK

 

[Gray0689]

If there is an undersizing issue then you could maybe consider installing a separate boiler for the water alone? That may work out cheaper than rejigging, IF that's required? I'd still like to know what circulating temps you're getting with different scenarios. I've seen extremely large houses run on a 15mm one-pipe system work no problem ... but heyho! Not at the property so I'm not experiencing what the installer is! You could even potentially have an issue with the new appliance that's starving the installation of heat? I could throw a few more 'possibilities' in the pot, none would be of benefit to be honest! Striping it back to basics you need to know (A) that there's enough heat being produced; you can then look at circulation and balance if you have (A)... If you haven't got (A) then there's a possibility that when the heating comes on it 'sucks' the heat out of the cylinder, the coil in effect works in reverse as colder primaries draw heat FROM the cylinder resulting in colder hot water .... Monitoring primary F&R temperatures can tell you a great deal about how well the demands are being met ....IMHO 🙂

May be a cheaper way to

 

[Centralheatking]

Just a quick question Grey 0689 but How do you cope sharing the same Island with Jon Cropp ?

he is my friend but I feel safe knowing its ferry ride away CHK

Mind you we are visting Feb as we have a contract 3 vans and
we are staying at Croppies !

May be a cheaper way to

 

[Gray0689]

Just a quick question Grey 0689 How do cope sharing the same Island with Jon Cropp ?

he is my friend but I feel safe knowing its ferry ride away CHK

Where both too blow ins
And he a southern softy too lol

 

[Gray0689]

Just a quick question Grey 0689 but How do you cope sharing the same Island with Jon Cropp ?

he is my friend but I feel safe knowing its ferry ride away CHK

Mind you we are visting Feb as we have a contract 3 vans and
we are staying at Croppies !

Lol croppie take you to a few good spots I'm sure lmao

 

[diamondgas]

Looks to me like Diamond gas has got it right - its a nice set up but underpowered
just go get another boiler and hook it in as suggested CHK

Its been a great post 10 pages and 35 likes and we all have
learned from it thank you CHK

To be honest CHK I've no idea whether it's undersized or not ... reading others more up on sizing seems to indicate an issue. The only way I see knowing for sure would be to monitor F&R temps. If a boiler is undersized it will be working flat out but flow temps will never get close to max for ages, if at all! OP did mention 71degC .. Not that hot in my experience.

If I was to offer a workaround for now I'd suggest a pipe stat on the primary flow linked in series to the hot water timing and zone valve allowing water to be heated only if the primary flow temp was above, say, 60 DegC?

 

[Howsie]

Chuck an ATAG or Viessmann in. 😉

 

[Carrera]

Hi, all and thanks for the feedback and suggestions to date, thought I'd give an update, I'm learning too so bare with me, although I like technical things. Also I am glad that people are finding it interesting. I will not stop posting until is is resolved, in the hope someone learns something, mainly me at this rate.


With your help the plumber has started to look at the flow issues
Where are we
In order to leave something working for xmas the magna was removed and replaced with now two small pumps, one replacing the magna and one on the flow return just under the bolier, system flushed through removing air
told not to use for than 3 manifolds at a time, and heat water separately.
they will be back early in the new year, accompanied by a consultant/design engineer.


has the system ever worked?
originally a year ago, the whole heating was running at 22c to dry the house, and it kept it there, however I did not monitor flows at that time.
also only used parts of it since some of the house is not complete
hot water with heating, found issue when we moved in after water was only ever Luke warm
towel rails I have not really used it can draw into mix, but at the moment leave to one side
bolier sizing was done by the energy consultant based on heat loss, trying to get an e copy of the numbers for those who are interested


How's it working
hot water only, starts off heating fine, but as cylinder gets warmer boiler starts to cycle every 2 mins for quite some time until the cylinder stat eventually switches everything off.
3 manifolds I tested yesterday work fine, flow rate at ports varying between 1.5 to 2 l/pm, with 40 to 42c flow and 30 to 32c return at each manifold. Got temp in heated areas to 21 to 22 within a couple of hours and switched off at around 2pm, outside temp 6c, never came on again for the rest of day, morning temp in those heated areas ranges between 19 to 21 depending on room as some have lots of glass, overnight temp 0c, only just switched on the now to top up.


boiler working very gently, output temp of 71c


manifolds. M1, 9 ports, m2 9 ports, m3 10 ports, m4 8 ports, m5 10 ports, m6 5 ports
flows up to heating are, first one is m2 and m3, second one is m1, m4 and m10
m6 is the basement and flows off the piping to the cylinder


Time to do some scenario testing if I can, happy to take suggestions and I can post results.


boiler temperature can be turned up, it on setting 5 and a bit at the moment give 71c?


flow and return temps under what scenarios? Easiest way to measure the temp? I have an ir thermometer, but how to get it to work on copper?if reliable at all?


manifold combinations, can switch all on to see what happens or one at a time?


best to have some results on the table before the guys come back to help get to a solution, whether it be a complete rehash, or mods to existing


merry xmas by the way and once again thanks.

 

[Chalked]

Merry xmas
How clean/ dirty was the water when the pump was taken out?

Hope the consultant can sort it

 

[Howsie]

Are you paying for the consultant?

 

[Carrera]

Merry xmas
How clean/ dirty was the water when the pump was taken out?

Hope the consultant can sort it

There was a little rubbish, not much really. Chemical cleaner was being used, then flushed through for quite a while.

 

[Ermintrude]

Like I said before isolate manifolds get flow to cylinder hot, so hot u cat touch , leave hot taps running so that cylinder is full of cool water. Turn on say m1 then wait, once return from m1 ok leve it on and turn on m2 keep going until the flow to cylinder cools so u can hold it.

Temps are relative so just wrap a thermometer in a cloth soaked on veg
Oil on pipe. Just enough cloth to hold bulb against pipe . Oil is just to conduct heat as water will evaporate .
Or buy a flexible plastic ones and stick to pipes , the film types.

Each manifold has it's own pump right? - stupid question but needs to be asked?

I think your plant room needs re configured, 100% LLH with pump set to each circ. cylinder fine , get zone valves fitted on each flow in plant room . Ie to each manifold or cylinder. Shouldn't require any disturbance outside of plant room. I would be fitting an additional boiler or boilers tho . My mind u want at least 70kw for peak demand . Won't say this too loud as not a fan of wb but put same boiler in as what u have or fit multiple new boilers say 2 or 3 ideal logic system 30kw or even two kestons as same boiler but higher output avail.

Don't forget to balance system and lag it properly

 

[Carrera]

Like I said before isolate manifolds get flow to cylinder hot, so hot u cat touch , leave hot taps running so that cylinder is full of cool water. Turn on say m1 then wait, once return from m1 ok leve it on and turn on m2 keep going until the flow to cylinder cools so u can hold it.

Temps are relative so just wrap a thermometer in a cloth soaked on veg
Oil on pipe. Just enough cloth to hold bulb against pipe . Oil is just to conduct heat as water will evaporate .
Or buy a flexible plastic ones and stick to pipes , the film types.

Each manifold has it's own pump right? - stupid question but needs to be asked?

I think your plant room needs re configured, 100% LLH with pump set to each circ. cylinder fine , get zone valves fitted on each flow in plant room . Ie to each manifold or cylinder. Shouldn't require any disturbance outside of plant room. I would be fitting an additional boiler or boilers tho . My mind u want at least 70kw for peak demand . Won't say this too loud as not a fan of wb but put same boiler in as what u have or fit multiple new boilers say 2 or 3 ideal logic system 30kw or even two kestons as same boiler but higher output avail.

Don't forget to balance system and lag it properly

each manifold has its own pump at the manifold not in the plant room. Manifold picture earlier in the thread.

 

[Ermintrude]

each manifold has its own pump at the manifold not in the plant room. Manifold picture earlier in the thread.

Hi, sorry on an iPhone.

Ok so you have zv on each manifold.
Don't like the 4 port blending valves. Difficult to balance. I prefer pump/ manifold return and primary flow. And then a balance-able return. Notice there is no pipe stat to tell the zv when flow is needed. So it's just open when manifold is on? Not much point in it. IMO , should have a pipe stat set on the returns from floor to blending valve and be set so that when flow cools and blending valve opens up for more primary heat and interlocks with boiler or in your case the LLH pump.

Also what is floor construction? Just that there is no conduit on the ufh pipes as they leave the floor? Always try and have 150mm of conduit above floor and 350 is below to protect from mechanical damage.

 

[JusKel]

View attachment 16396
Don it albeit sideways!
this is the plant room setup

If that is the main pump, then why is there a tee between it and the boiler?
Can you remove it and connect in to left side of pump ?
Or maybe move the pump onto the pipe coming directly off the boiler?
(Mentioned previous too)

 

[Jedny]

Any chance of bigger pic

 

[Ermintrude]

Any news?

 

[diamondgas]

Hi Carrera, To get the IR working you can paint the pipe black 🙂

Scenarios with testing .... I'd want to know what strain was being put on the boiler, so primary F&R's would be where I'd monitor under as many load scenario's as possible up to max load. If your flow temp drops below 60 DegC it'll start to draw heat out of the cylinders hot water. If the flow temp stays cool for a long time then I'd be pointing towards that being the reason why your hot water isn't getting to temp!

If you haven't already, I'd put the hot water on 24/7 or at least an all day setting.... 🙂

 

[Carrera]

Sorry haven't been able to test much at all, as the system is not really working as it was left for the holidays. At the moment just about able to get warm water, boiler going on and off very 2 mins and the heating was working with a light load, but has now started doing the same. Will have to wait for the plumber to come back next week before I can really try anything

 

[diamondgas]

Give Worcester a call, your boiler is under warranty with them. You may have a fault on the boiler?

 

[Carrera]

Give Worcester a call, your boiler is under warranty with them. You may have a fault on the boiler?

For the hot water, basically boiler fires, flow temp rises (set to 70), modulates lower and lower and kicks off when it goes over 70, water circulates for a couple of mins and then when temp hits about 40 boiler fires again, slowly getting to 70, before we go back round the loop. As you can imagine water takes ages to warm up this way, so have been combining thus with the emmersion over the holidays. I will give wb a call on Monday.

does not do this on heat, gets to 70 and stays there, however this morning started doing above with heating, but after a few attempts of me stopping and starting the heat, it appears to be ok.

 

[diamondgas]

For the hot water, basically boiler fires, flow temp rises (set to 70), modulates lower and lower and kicks off when it goes over 70, water circulates for a couple of mins and then when temp hits about 40 boiler fires again, slowly getting to 70, before we go back round the loop. As you can imagine water takes ages to warm up this way, so have been combining thus with the emmersion over the holidays. I will give wb a call on Monday.

does not do this on heat, gets to 70 and stays there, however this morning started doing above with heating, but after a few attempts of me stopping and starting the heat, it appears to be ok.

Without seeing what's going on it's difficult to give you anything accurate to be honest Carrera! Are you able to get a reading on the return as the flow is heating? If so there should be around 20DegC difference, thereabouts. If there's a rapid rise in temp to 70 before dropping back to 40 then I'd be wanting to know how well the pump was performing and/or is there a potential flow restriction somewhere? If the rise is gradual and there's a maintained 11-22DegC difference between F&R then Circulation is okay IMHO 🙂

 

[Howsie]

This one really needs eyes on IMHO.

 

[Gray0689]

This one really needs eyes on IMHO.

I agree something just ain't right even apart from the under sizing IMO

 

[diamondgas]

:iagree: without 1st hand knowledge there's strange goings on being described...! It'd be handy to have to op's plumber on here to give us the heads up on what they've done so far! Doubt they'd like some of the chatter in the thread mind! 🙂

 

[albatross]

Carrera, I have a good read of this and it's the kind of problem that needs a site visit. It's a shame you are so far from me, I'm in Yorkshire, as I would have liked to have got my teeth into it and solved it for you. Saying that try this:

Turn hot water on, turn one underfloor manifold on upstairs, close all the lever valves at the top left of the photo, see if the cylinder heats, if so you have a severe balancing problem.

This may make no difference but it's worth trying. Modern cylinders have high resistance coils and the circuit to the manifolds will have a low resistance as the underfloor pumps take over the work after that.

 

[huddster]

Would it not be worth putting some gate valves on before the lever valves to restrict the ufh circ and towel rads to test weather it is drawing the heat away from the hot water, just a cheap option that might get you by until you figure out a more permanent solution

 

[Ermintrude]

Could just close ball valves ?