Indirect Unvented cylinder, Combi Boiler and Nest Thermostat

[Chris1012]

We have just had an indirect unvented cylinder (250l Vertical Telford Tempest) installed along with a nest v3 thermostat.
The plumber was able to modify our existing combi boiler, so it runs like a system boiler.

I am trying to understand how it works as currently the plumber has set it to come on for 2 hours each day (1hour between 5am-6am and 5pm-6pm).
During these times, the boiler remains continuously on and only switches off after the hour mark.
Is this right?
I would have thought during the set times that the boiler should come on, it would work in connection with the cylinders thermostat so once the waters heat got to a set level, the boiler will shut off.

The cylinders booklet states it takes 28min for it to heat up.

Could someone please advise on how this setup should be working and if there is anything I could do to make it more efficient, then it currently is?

Thank you

 

[ShaunCorbs]

Any pictures of the set up ?

 

[Chris1012]

Any pictures of the set up ?

I can take some but the boiler is located in the kitchen and there is shelf above the pipes, so wont be able to see anything and the cylinder in the basement.

 

[Chris1012]

Another potential issue is that it takes 45-60seconds to get hot water from the taps.
The route for the mains water supply enter the kitchen, goes through a water softener then travels 5 meters to the cylinder and then is routed to the rest of the house...

 

[sparkie30]

You are correct the boiler should turn off when cylinder stat satisfied.

Should be wired like this from nest to cyl stat,
Stat to 2 or 3 port valve and then to boiler.

Sounds like plumber has wired straight from nest to boiler thats the reason is on for full hour.

Good luck

 

[Chris1012]

Looks like the gas light comes on the boiler during the schedule to heat the tank but once it reaches the correct temp, the gas light goes off (so does the flame) but the boiler continues to run with the rad light on until the scheduled time is over.
Does this sound right?

Also does the 45sec heat up time to each tap and shower, sound right?
Length to each service is no more than 6meters, using a 22mm flexi pipe

 

[Scott_D]

Pictures needed

 

[Bibbs118]

Combi on an invented, I've scene these sort of installs before and your asking for trouble in my opinion.

If I where you, I'd ring the boiler manufacturers and ask them if their combi can be installed on a invented, I very much doubt they will say yes.

And if they do say yes, ask them to email you a wiring and piping diagram, if they are unable to provide you with a drawing, then, despite the tech help line saying it is "possible", without a drawing it is NOT approved. And probably dangerous.

 

[ShaunCorbs]

Combi on an invented, I've scene these sort of installs before and your asking for trouble in my opinion.

If I where you, I'd ring the boiler manufacturers and ask them if their combi can be installed on a invented, I very much doubt they will say yes.

And if they do say yes, ask them to email you a wiring and piping diagram, if they are unable to provide you with a drawing, then, despite the tech help line saying it is "possible", without a drawing it is NOT approved. And probably dangerous.

Why it's just another heat load prividing you have a draw off eg a tap off the combi your fine

 

[Bibbs118]

Why it's just another heat load prividing you have a draw off eg a tap off the combi your fine

Because without a drawing, it not installed to manufacturers instructions.

Min AR.

Always say on first page, MUST BE INSTALLED TO MANUFACTURERS INSTRUCTIONS.

 

[ShaunCorbs]

Because without a drawing, it not installed to manufacturers instructions.

Min AR.

Always say on first page, MUST BE INSTALLED TO MANUFACTURERS INSTRUCTIONS.

Your joking right nothing to do with gsiur/p

 

[Bibbs118]

Your joking right nothing to do with gsiur

No, if it say, MUST BE INSTALLED TO MANUFACTURERS INSTRUCTIONS, and the manufacturers can't provide INSTRUCTIONS how to install an invented on a combi then you are NOT REPEAT NOT installing it to MIs.

If it says MUST BE INSTALLED TO MANUFACTURERS INSTRUCTIONS unless your bolting a invented cylinder to combi, in that case you can just make it as you go along, or ask your mate how to do it. Then it's fine.

 

[Bibbs118]

Ask yourself this question.

Has it been installed to MIs?

If MIs don't give you INSTRUCTIONS how to do a invented combi install.......Then it's not been installed to MIs has it.

 

[ShaunCorbs]

How is any of that ar

guess they tell you what brand / type of rads to install as well

 

[Bibbs118]

You are correct the boiler should turn off when cylinder stat satisfied.

Should be wired like this from nest to cyl stat,
Stat to 2 or 3 port valve and then to boiler.

Sounds like plumber has wired straight from nest to boiler thats the reason is on for full hour.

Good luck

So thats no temperature control or safety shut off on an invented cylinder!!!! What could possibly go wrong?

 

[ShaunCorbs]

So thats no temperature control or safety shut off on an invented cylinder!!!! What could possibly go wrong?

And how does that make it a nono to install with a combi boiler

Ffs

 

[Bibbs118]

How is any of that ar

guess they tell you what brand / type of rads to install as well

All boilers are designed to be installed as per MIs, if it's not installed to MIs and it's ncs are no longer applicable then it's AR.

SERIOUSLY..........THERE IS A REASON WHY ON THE FIRST PAGE OF EVERY INSTRUCTION MANUAL IT SAYS MUST BE INSTALLED AS PER INSTRUCTIONS. Never say, if you think you know better than us ( manufacturers) just crack on, do what want, install it how you think.

Do you not remember being constantly told during training ALWAYS FOLLOW MIs?

 

[ShaunCorbs]

All boilers are designed to be installed as per MIs, if it's not installed to MIs and it's ncs are no longer applicable then it's AR.

SERIOUSLY...THERE IS A REASON WHY ON THE FIRST PAGE OF EVERY INSTRUCTION MANUAL IT SAYS MUST BE INSTALLED AS PER INSTRUCTIONS. Never say, if you think you know better than us ( manufacturers) just crack on, do what want, install it how you think.

Do you not remember being constantly told during training ALWAYS FOLLOW MIs?

Will put it this way

Does it say not to install one in combination with an unvented cylinder no it doesn't

Not everything is in the manufacturers instructions

 

[Bibbs118]

And how does that make it a nono to install with a combi boiler

Ffs

Because unless the manufacturers of the combi say it can be installed on an unvented they how can you follow the mis?

 

[ShaunCorbs]

Because unless the manufacturers of the combi say it can be installed on an unvented they how can you follow the mis?

They don't govern/ say what type of heat load you must have

I could install one to a pool still would be installed correctly and manufacturer would still warrenty it

 

[Bibbs118]

Will put it this way

Does it say not to install one in combination with an unvented cylinder no it doesn't


Not everything is in the manufacturers instructions

This is why I did write, ring them an ask for a drawing, no drawing and you can not be following MIs, and the instructions ALWAYS say MUST BE INSTALLED TO MANUFACTURERS INSTRUCTIONS.

AND NEVER SAY, unless you think you know better.

 

[ShaunCorbs]

I give up

@Harvest Fields @townfanjon @Best @sammathias @hammers4spanner @Riley @jtsplumbing

Am I wrong again ?

 

[Bibbs118]

I give up

@Harvest Fields @townfanjon @Best @sammathias @hammers4spanner @Riley @jtsplumbing

Am I wrong again ?

Yes or no?

Do you have to install to MIs?

 

[Harvest Fields]

Why it's just another heat load prividing you have a draw off eg a tap off the combi your fine

I have a regular customer who has moved house to a house with a Vaillant combi on a Vaillant unvented cylinder. He had me in to have a look but as Shaun has this this ones hot supply has just been capped off. So I am going to run a short run of pipe and a hot tap to the garage or inside the utility.

 

[Harvest Fields]

I give up

@Harvest Fields @townfanjon @Best @sammathias @hammers4spanner @Riley @jtsplumbing

Am I wrong again ?

I’m with you mate. Next he will be saying you cannot Zone a heating circuit? No difference between another zone and a zone for the cylinder. Seen it done loads. Would make sure it has a hot water draw off though. I spoke to Vaillant on the one my customer has as there is loads of work needed and they said just fix the issues and make sure it has a hot water draw off. I’m happy with that.

 

[Harvest Fields]

Yes or no?

Do you have to install to MIs?

I’m sure there is nothing in the Vaillant manual that shows you how to pipe in 2 zones for a larger house yet Vaillant say you can fit their 938 into a 4 bed semi with a bathroom and ensuite. So does that mean on a new build you would put the whole system on one zone? @Bibbs118

 

[Bibbs118]

Look, you are missing the point, one, seeing it done loads does not mean it's OK, two, vaillant will have a drawing for an s plan plus, three, doing it so it's safe in your mind is not the same as installing to MIs.

And four. Yes or No, do you have to install to MIs?????

If there is no instructions then how can you follow them, this is why I did say, get a drawing from the manufacturers .

 

[hammers4spanner]

You can put a combi on unvented have seen it done numourous times . One hot draw off to utility basin in most cases.

Even done a greenstar with a worcester enginger couple year ago.
If anyone would know about their product they would.

As said another heat source.

 

[Harvest Fields]

Look, you are missing the point, one, seeing it done loads does not mean it's OK, two, vaillant will have a drawing for an s plan plus, three, doing it so it's safe in your mind is not the same as installing to MIs.

And four. Yes or No, do you have to install to MIs?????

If there is no instructions then how can you follow them, this is why I did say, get a drawing from the manufacturers .

You’ve answered you own question. If they have a schematic for an s plan then yes you can.

 

[Bibbs118]

You can put a combi on unvented have seen it done numourous times . One hot draw off to utility basin in most cases.

Even done a greenstar with a worcester enginger couple year ago.
If anyone would know about their product they would.

As said another heat source.

Please re read what put. Seeing it loads off times does not meant it's OK, this is why I did say get a drawing.

And , s plan zones don't require temp and pressure relief of or a temp cut off do they? So not the same .

 

[Bibbs118]

Yes or no, do you have to install to MIs?

 

[ShaunCorbs]

Ffs 😱

 

[Harvest Fields]

Think we have to just disagree on this one @ShaunCorbs 😀😀😀@Bibbs118. I trust what Vaillant told me and that’s that.

 

[Harvest Fields]

Please re read what put. Seeing it loads off times does not meant it's OK, this is why I did say get a drawing.

And , s plan zones don't require temp and pressure relief of or a temp cut off do they? So not the same .

No idea what world you live in though mate.

 

[Bibbs118]

Think we have to just disagree on this one @ShaunCorbs 😀😀😀@Bibbs118. I trust what Vaillant told me and that’s that.

Being told something is not the same has following the MIs, what am saying is, if you can't get a drawing then it's not ok .

Because it's impossible to follow MIs without having the MIs .


Just ask yourself the yes or no question and the answer will tell you what I'm saying is correct .

Do you have to install to MIs? Yes or NO

 

[Harvest Fields]

Being told something is not the same has following the MIs, what am saying is, if you can't get a drawing then it's not ok .

Because it's impossible to follow MIs without having the MIs .

If the manufacture say it is ok. And they warrant the job for 10 years then it is ok. But for future reference I will make sure they email me confirmation.😛😛 On that not I’m done. I will not be commenting again.

 

[Bibbs118]

If the manufacture say it is ok. And they warrant the job for 10 years then it is ok. But for future reference I will make sure they email me confirmation.😛😛 On that not I’m done. I will not be commenting again.

That's totally correct, you need confirmation.

 

[Harvest Fields]

That's totally correct, you need confirmation.

I was being sarcastic. 😀😀 But honestly I’m done now

 

[hammers4spanner]

Re read what I wrote.

I have done this with a worcester engineer employed by worcester.
It is acceptable.

 

[townfanjon]

Just come in on this one , will read it all later , just back off holiday, FFS phones going mad .

 

[Bibbs118]

Re read what I wrote.

I have done this with a worcester engineer employed by worcester.
It is acceptable.

So worcester can authorise an invented cylinders on say a vaillant combi or baxi?????

 

[Bibbs118]

I was being sarcastic. 😀😀 But honestly I’m done now

If you don't have it in writing then you are not following instructions are you .

Just answer questions

YES OR NO DO YOU HAVE TO INSTALL TO MIs?

 

[hammers4spanner]

Can worcester authorise one of their own products ?
Of course they can .
A worcester was fitted on such set up and fitted and authorised along with guarantee themselves.

Job done money in the bank and all happy

 

[Bibbs118]

Can worcester authorise one of their own products ?
Of course they can .
A worcester was fitted on such set up and fitted and authorised along with guarantee themselves.

Job done money in the bank and all happy

That ok, am not saying it can't be done, am saying the poster needs a drawing, if no drawing is available then it's not permitted .

And saying I've seen it done loads of times does not mean it's right, I've seen loads of flue not clipped but that doesn't mean it's right .

 

[ShaunCorbs]

You don't need a drawing / tech schematics

Doesn't mean it's unsafe or manufacturer arnt going to warrenty there boiler

Hell even if you fit the unvented incorrectly I'm sure they would still warrenty there boiler

 

[Bibbs118]

You don't need a drawing / tech schematics

Doesn't mean it's unsafe or manufacturer arnt going to warrenty there boiler

Hell even if you fit the unvented incorrectly I'm sure they would still warrenty there boiler

So what your saying you DONT need to install to manufacturers instructions? Interesting.

 

[ShaunCorbs]

So what your saying you DONT need to install to manufacturers instructions? Interesting.

More like common sense

 

[hammers4spanner]

In all honesty I would say 90 % of boilers I cone across are not installed as per MI

 

[Bibbs118]

More like common sense

The as long as you use common sense you don't have to follow MIs?


What if your common sense differs from my common sense. Because my common sense says always and without exception install to MIs, but you your common sense says something different

 

[Best]

I am not gas qualified, so won’t comment on anything gas.
The unvented cylinder will be to regs if heated by a controlled heat source of oil or gas boiler and the 2 port valve supplied with the unvented unit to be in operation, controlled by uv stat.
A combi used with extra zone, or solely a zone for unvented or vented cylinder hot water I would have thought was fine and to MIS.
The space heating main body part of a combi boiler is just the same as a heat only system boiler anyhow, - isn’t it?
But sure it only takes a phone call or email to the boiler manufacturer to confirm.
I know combi boilers are installed on homes where there is some sort of hot water cylinder (vented or not) so to give option of mains pressure hot water at some outlets, or to provide instant hot water at a supply close to where the gas boiler is sited, - like a kitchen tap.

 

[Chris1012]

So many posts on here now, hard to keep up and on topic.
Does this mean it should or should not take 40seconds to get hot water from the taps?

 

[Bibbs118]

Something that is always over looked on these installs is if the dhw draw off from the combi is to a frequency used hot tap, the boiler sits in anti cycle for 5 mins every time the flow turbine moves, meaning it can take hours to heat the cylinder.

 

[Chris1012]

As requested, Pictures from the cylinder. Seems the hot feed from the top of the cylinder is branched off - 1. Specifically to the upstairs bathrooms x 2 (1st floor and loft).
2. The rest of the house

 

[Best]

Who lagged the discharge pipes?
Also I would get that plastic push fit stopend replaced with a brass compression stopend

 

[Chester]

Ew, polyplumb

 

[Welder]

Wonder if they wore a wool shirt too...😱 Who the hell puts that rubbish on. Especially in a cold space like a basement...

 

[Scott_D]

Any pictures of under the boiler, 2 port valves etc around the cylinder

It is insulated, not they way most would do it but I don't think it specifies anywhere what standard if insulation must be used?

 

[Welder]

It's about appropriateness. If that space get s down around freezing then it needs better protection.
If however it's to protect against rodents, then that works brilliantly as they don't like the fibrous nature of it and leave it alone... Instead they use the polyplumb elbows to sharpen their teeth 😀

 

[Chris1012]

Any pictures of under the boiler, 2 port valves etc around the cylinder

It is insulated, not they way most would do it but I don't think it specifies anywhere what standard if insulation must be used?

Unfortunately not, as the pipes from the cylinder are all under the panel that has been fixed back to the cupboard.

The location of the boiler is within the kitchen.

I believe there is a 3 port valve, 2 of the ports are for underfloor heating within the kitchen/diner area.

 

[Chris1012]

It's about appropriateness. If that space get s down around freezing then it needs better protection.
If however it's to protect against rodents, then that works brilliantly as they don't like the fibrous nature of it and leave it alone... Instead they use the polyplumb elbows to sharpen their teeth 😀

Never gets below around 15 degrees

 

[Best]

I am surprised if MIs state just 28 minutes for that cylinder reheat.??? I would have thought it is much more.
The hot water outlet on unvented cylinders I prefer to drop the pipe before ever raising the pipe to a higher level. Just raising a hot outlet will mean some of the stored heat from the cylinder will keep heating the water in the raised pipe, therefore wasting energy.

 

[ShaunCorbs]

I am surprised if MIs state just 28 minutes for that cylinder reheat.??? I would have thought it is much more.
The hot water outlet on unvented cylinders I prefer to drop the pipe before ever raising the pipe to a higher level. Just raising a hot outlet will mean some of the stored heat from the cylinder will keep heating the water in the raised pipe, therefore wasting energy.

20kw going into the coil will re heat in around 30 mins

 

[Best]

20kw going into the coil will re heat in around 30 mins

I am going to check the MIs on Telfords.
I thought they claimed it to be much longer.

 

[Chris1012]

From the Telford user manual

 

[ShaunCorbs]

That's the direct on have a look at the indirect spec

 

[Best]

35 minutes for full reheat, is what I read on 250l indirect.
Not bad, if that's correct.
I have one installed isn't achieving that

 

[ShaunCorbs]

35 minutes for full reheat, is what I read on 250l indirect.
Not bad, if that's correct.
I have one installed isn't achieving that

Size of boiler ?

 

[Chris1012]

That's the direct on have a look at the indirect spec

That was indirect. My cylinder is 250l

 

[Best]

Size of boiler ?

30kw WB gas boiler. It is my partners house, so something I am aware of. Pipework all mine, except the gas, so no bother there.
I need to investigate it more.

 

[Best]

That was indirect. My cylinder is 250l

View attachment 33580

Yes, I got same on searching. 35min from cold to 60 degrees

 

[ShaunCorbs]

30kw WB gas boiler. It is my partners house, so something I am aware of. Pipework all mine, except the gas, so no bother there.
I need to investigate it more.

Yea should be able to heat that no problem

 

[Welder]

What flow temp is that at tho?
I've just installed twin 150L OSOs and they state recovery rates at 80 degs flow!! Still, makes it look good 😱

 

[Chris1012]

What flow temp is that at tho?
I've just installed twin 150L OSOs and they state recovery rates at 80 degs flow!! Still, makes it look good 😱

How can the flow rate be confirmed/checked?
The cylinders temp is around 65c

 

[Welder]

Its the boiler flow temp that OSO quote at 80 degs. Most boilers closer to 70 so recovery rate way longer than stated depending on coil design (ability to transfer heat).

 

[Chris1012]

Its the boiler flow temp that OSO quote at 80 degs. Most boilers closer to 70 so recovery rate way longer than stated depending on coil design (ability to transfer heat).

apologies for my ignorance, I am not technical at all.
My understanding was once the cylinder is heated up, the outlets would draw the hot water from the cylinder and not the boiler anymore...?

 

[Welder]

We are at cross purposes.

The outlets do indeed draw their water from the cylinder. As the stored HW is used then temperatures at the outlets reduce.

What I was talking about was the time taken for the temps to recover (go back up). Most manufacturers give an indication of the time taken to heat a cylinder of cold water to approx 60 degs C. To understand whether this is realistic (indicative of the world we inhabit not the one manufacturers inhabit) we need to know the temp of the water going in (the lower the temp (say winter) the longer the recovery time, and the temp of the heating water through the coil. Most heating coils operate at approx 70 deg C buit the one I was referring to said it assumed a heating coil temp of 80 degs C. Frankly its unrealistic.

Bottom line. Take ALL numbers issued by manufacturers with a BUCKET of salt. YOUR circumstances dictate what will happen as every installation is different.

HTH

 

[AWheating]

The cylinder will only heat up at the time in the instructions in ideal conditions. Unlikely in real world situations. Time the hot water to be on without the heating so it's coil gets the boilers full output and it won't take too long. Have the heating on and it will get a share of the boilers output. Best to set hot water to come on one hour before heating times.

 

[AWheating]

a combi with an unvented cylinder is fine, all manufacturers will happily agree to this. Most manufacturers will have a drawing showing there boilers with cylinders. They won't show the full technical spec of an unvented cylinder of course as that's down to the cylinders manufacturer to spec.

 

[Chris1012]

The cylinder will only heat up at the time in the instructions in ideal conditions. Unlikely in real world situations. Time the hot water to be on without the heating so it's coil gets the boilers full output and it won't take too long. Have the heating on and it will get a share of the boilers output. Best to set hot water to come on one hour before heating times.

During last weeks heat wave, I was testing the hot water at each outlet. As the weather has been pretty mild since last week, the heating has not been on at all.
When I am testing the hot water at each tap, no other service is in use, including rads or UFH.
However it seems to still be the same heat up time from last week until today - average of 40seconds to get hot water!

 

[Welder]

Ahh. Is what you are talking about is the time for the hot water to reach the taps? If it is there is nothing you can do without massive investment. This would be the same issue regardless of whether an Unvented cylinder or combi is installed in the same place. It is a product of the distance the water has to travel and an UVC cannot, for obvious reasons, be located as closely as say a combi can in a kitchen.

 

[Gasinspect]

We now fit a circulating pump on the hot water from the cylinder. Combi heats it fine, all hot water taps from cylinder so no time lag. Put circulator on a ceiling mounted proximity sensor so that runs for 15 minutes when activity in the bathroom area. The kitchen sink near enough not to need circulation.

 

[ShaunCorbs]

We now fit a circulating pump on the hot water from the cylinder. Combi heats it fine, all hot water taps from cylinder so no time lag. Put circulator on a ceiling mounted proximity sensor so that runs for 15 minutes when activity in the bathroom area. The kitchen sink near enough not to need circulation.

You mean a src (secondary return circuit)

 

[Welder]

Im assuming that too Shaun. Fact is tho that is not always an option. Plus, in its life, it wastes huge amounts of energy if its a retrofit because no pipework will be insulated. Frankly its cheaper to waste water.

 

[dan_the_plumber]

Combi on unvented is fine. If you’ve got your 2 port valve and all other G3 kit installed correctly then there nothing wrong with that at all. Assuming it’s installed correctly the coil is just like another radiator

 

[Harvest Fields]

Combi on unvented is fine. If you’ve got your 2 port valve and all other G3 kit installed correctly then there nothing wrong with that at all. Assuming it’s installed correctly the coil is just like another radiator

That’s also what we were saying mate😀😀