UFH not getting hot on vented system

ejkilby1 · Dec 13, 2021

Hi folks, I’m in need of some sound advice.

We have recently had a ground floor extension and have had underfloor heating (company: JK UFH) installed throughout most of the downstairs. We have a few rads still left downstairs and the entire upstairs is still heated through rads.

We have a vented (gravity fed) central heating system (about 0.3 bar), heated from an oil fired Thermecon boiler. The header tank is in the loft and the boiler in the garage. It’s an S plan setup with two 2 port valves that control the flow to the CH and to the water heater tank (immersion).

The plumbers have just connected the UFH as a direct T -off from the flow (just after the boiler) and the return just before the boiler, as the UFH manifold is in the garage also.

The UFH has not been placed on a separate thermostat or controlled with a separate port valve, therefore it’s a dumb system and will only receive hot water if either the hot water tank or the CH are calling for heat. My plan is to get it on its own zone, however as things stand, I simply can’t get it to get hot at all. The best I’ve managed is 30 degrees while the boiler is running.

The pipework from the boiler to the manifold and CH is 22mm and all rads are on 15mm

My understanding is that I have the following options, however I’m a little in the dark as to the best course of action, so any advice and opinions would be welcome.

I’m told that an additional pump is needed to get the hot water sent to the UFH manifold, however where would this pump go? before or after the T-off to the UFH manifold? Also, would a second pump run the risk of over pumping into the header tank, adding crap into the system? Or should this pump replace the current one on the first floor.
Install more valves to enable the UFH to be diverted all hot water at the times it requires it, therefore going from a 2 valve to a 3 valve system. I’m thinking this will mean that the UFH will only get hot if the others are not calling for heat.
Make the CH system unvented (pressurised) with an expansion vessel and filling loop. My worry here is that pressurising the system might find weakness in the pipework (house was built in 1990). Also I’m guessing that even after this is done, I still need to zone the UFH onto its own circuit.
I’ve read that Installing a plate heat exchanger to the UFH would add pressure and get the heat through the system, however I’ve no Idea if this is a valid option and I’m assuming I still need to zone the UFH off.
Some combination of the above

I have attached an image of my setup. I’m not a plumber so please let me know if I have missed some crucial piece of information here.

Edd

Deleted member 120897 · Dec 13, 2021

Have you thought about getting the company back who installed the ufh system? Challenge them with the questions asked on here, as they’ve now left you with a system that doesn’t heat up as you want.

exedon2 · Dec 13, 2021

If your pipework layout is as you have sketched it out it's wrong .
Get installer back to sort it.

ejkilby1 · Dec 13, 2021

Undertrained said:
Have you thought about getting the company back who installed the ufh system? Challenge them with the questions asked on here, as they’ve now left you with a system that doesn’t heat up as you want.

The company that installs the system unfortunately don't connect them to your existing system, they leave it for you to get plumbers into connect it. The company is jk-gb.com I have had some plumbers in to connect it, but they didn't do anymore than T-off from the main line and as you have to bring it up to temp very very slowly, they wouldn't have known on the day if it was or wasn't really heating well (it does get up above 25 degrees). The plumbers used are now booked up for months and I'm keen to get some advice on options. I will either be getting the same plumbers back or see if I can get a UFH engineer to come and advise, but struggling to find someone with availability. I have spoken to JK and they have suggested an additional pump and valve, but not suggested where, and I've no idea of their ability to suggest this, not really knowing much about my setup. I won't be doing anything myself, but it would be useful to get some opinions on what might seem like a sensible solution, given there seems to be so many options.

Cheers

Edd

ejkilby1 · Dec 13, 2021

exedon2 said:
If your pipework layout is as you have sketched it out it's wrong .
Get installer back to sort it.

Are you able to elaborate on specifically what you have seen that's wrong? It would be helpful to know ready for when someone does come back.

Deleted member 120897 · Dec 13, 2021

If it were me, I’d be checking to make sure it works as part of commissioning.

exedon2 · Dec 13, 2021

Connection to underfloor needs to be after existing pump with it's own zone valve and control.
Strictly speaking the underfloor return needs to be connected in before the cylinder return.
Advising a second pump shows a distinct lack of knowledge. could easily cause problems.
Converting to sealed system is worth considering move pump next to boiler tee in underfloor bring cylinder return back to make it last connection.

ShaunCorbs · Dec 13, 2021

Basically the plumbers don’t know what there were doing how is the manifold supposed to get flow / hot water from the system as it’s before the pump

Ask for a refund and get another heating engineer in

Best to seal the system eg unvented

Move the pump to before the ufh manifold and a plan plus the system

Then use heat miser controls for the ufh system

ejkilby1 · Dec 14, 2021

exedon2 said:
Connection to underfloor needs to be after existing pump with it's own zone valve and control.
Strictly speaking the underfloor return needs to be connected in before the cylinder return.
Advising a second pump shows a distinct lack of knowledge. could easily cause problems.
Converting to sealed system is worth considering move pump next to boiler tee in underfloor bring cylinder return back to make it last connection.

Thanks that's very helpful, are you able to explain further about the cylinder return coming last? what effect does this have? I have attached an image of what I think you are proposing, is this accurate?

ejkilby1 · Dec 14, 2021

ShaunCorbs said:
Basically the plumbers don’t know what there were doing how is the manifold supposed to get flow / hot water from the system as it’s before the pump

Ask for a refund and get another heating engineer in

Best to seal the system eg unvented

Move the pump to before the ufh manifold and a plan plus the system

Then use heat miser controls for the ufh system

Thanks for this. It's probably hard to advise, but what's the likelihood of me having issues if I pressurise the system. It's probably hard to say, but as plumbers is it a common issue to get issues changing from vented to unvented?

ShaunCorbs · Dec 14, 2021

It’s one of them can’t comment but you could pressure test it first to see if you will have any problems

Ric2013 · Dec 14, 2021

Do not do as your proposal sketch.

Looking at your sketch of the existing, the location of the system pump is currently correct and you mustn't move it. In theory, teeing off the boiler as you have done might have worked IF there were no other circuits, but there are.

There are such things as two pump systems but doesn't really make sense in your case and I see no need to convert to sealed if there are no other issues. UFH should work on a vented system.

If you want the UHF always on when other things are calling for heat, you need to tee in your flow after the pump (X), and tee in the return between the confluence of the cylinder/radiator circuits (X) and the boiler return inlet - where the return tee is currently should be fine. You may as well fit a zone valve on the flow while you are about it even if you don't wire this up immediately - just take the motorised head off and set to manual until you get around to re-wiring the controls (from the existing S plan to S plan+).

It may be worth placing an adjustable bypass between the UFH flow connexion and return connexion so you can have control of the temperature of the return water being sent back to the boiler (for system balancing purposes).

It may also be worth considering adding system biocide (eg Sentinel X700) to prevent bacterial build up in the UFH circuit. Plumbing paranoia here, but I suspect the increased use of UFH will give rise to issues until use of biocide becomes standard practice.

Surprised your plumbers didn't know most of this. Sure you didn't DIY install it?

EDIT - Are you sure your cylinder is plumbed that way around? Just out of interest.

ejkilby1 · Dec 14, 2021

Ric2013 said:
Do not do as your proposal sketch.

Looking at your sketch of the existing, the location of the system pump is currently correct and you mustn't move it. In theory, teeing off the boiler as you have done might have worked IF there were no other circuits, but there are.

There are such things as two pump systems but doesn't really make sense in your case and I see no need to convert to sealed if there are no other issues. UFH should work on a vented system.

If you want the UHF always on when other things are calling for heat, you need to tee in your flow after the pump (X), and tee in the return between the confluence of the cylinder/radiator circuits (X) and the boiler return inlet - where the return tee is currently should be fine. You may as well fit a zone valve on the flow while you are about it even if you don't wire this up immediately - just take the motorised head off and set to manual until you get around to re-wiring the controls (from the existing S plan to S plan+).

It may be worth placing an adjustable bypass between the UFH flow connexion and return connexion so you can have control of the temperature of the return water being sent back to the boiler (for system balancing purposes).

It may also be worth considering adding system biocide (eg Sentinel X700) to prevent bacterial build up in the UFH circuit. Plumbing paranoia here, but I suspect the increased use of UFH will give rise to issues until use of biocide becomes standard practice.

Surprised your plumbers didn't know most of this. Sure you didn't DIY install it?

EDIT - Are you sure your cylinder is plumbed that way around? Just out of interest.

Thanks for this, yes sadly I didn't DIY this install, but it's a little comical to hear that suggested based on what I'm currently facing.

Ok so based on what you're suggesting, I would need to get the flow moved to come from somewhere after the pump? if that's needed then that's a bit of a pain as the UFH is currently in the garage and to run a pipe over to where the pump is would require a number of ceilings to be taken down ☹️ from what I can tell/assume anyway

Thanks for the tip regarding the Biocide.

Regarding "Are you sure your cylinder is plumbed that way around?" I'm not sure I understand the question. In terms of the return, it's possible that it and the rads are the other way around, but without taking the ceiling down I don't think I can tell. Is that what you meant?

Attached is another diagram based on your suggestion above, please let me know if this is what you were suggesting?

Oh and regarding the comment "adjustable bypass between the UFH flow connexion and return connexion" They did install a differential pressure bypass value between the two, is this what you were thinking?

Kind regards

Edd

ShaunCorbs · Dec 14, 2021

Return is in the wrong place for the ufh as the cylinder needs to be the last return before the boiler 3 tee rule

Ric2013 · Dec 14, 2021

ShaunCorbs said:
Return is in the wrong place for the ufh as the cylinder needs to be the last return before the boiler 3 tee rule

True. But if the rads are currently the last return and it is not causing a perceptable problem, then surely making the UFH the last return won't make the situation any worse?

ejkilby1 said:
Ok so based on what you're suggesting, I would need to get the flow moved to come from somewhere after the pump? if that's needed then that's a bit of a pain as the UFH is currently in the garage and to run a pipe over to where the pump is would require a number of ceilings to be taken down ☹️ from what I can tell/assume anyway

Sadly, that was what I meant.

ejkilby1 said:
Regarding "Are you sure your cylinder is plumbed that way around?" I'm not sure I understand the question. In terms of the return, it's possible that it and the rads are the other way around, but without taking the ceiling down I don't think I can tell. Is that what you meant?

Usually the flow goes into the top of the cylinder coil and the cooler return comes out of the bottom of the coil. That is conventional, but there is a minority school of thought that it is better to go into the bottom, hence my interest.

If you are suggesting you don't know where the radiator circuit and cylinder coil circuit join, however, then bear in mind what Shaun and others are saying about the 'three tees rule'. What I've said previously is based on your diagram being correct.

ejkilby1 said:
Attached is another diagram based on your suggestion above, please let me know if this is what you were suggesting?

It is.

ejkilby1 said:
Oh and regarding the comment "adjustable bypass between the UFH flow connexion and return connexion" They did install a differential pressure bypass value between the two, is this what you were thinking?

No, I was thinking a fixed bypass really such as a gate or a globe valve as the return from the UFH will be much cooler than that from the radiators once the system is warm and I would want to prevent condensation occurring inside the boiler if the boiler is not a condensing boiler, and the potential of weird behaviour if the boiler is a condensing boiler but may respond to an unusually cool return in an undesirable way.

ejkilby1 · Dec 14, 2021

Ric2013 said:
True. But if the rads are currently the last return and it is not causing a perceptable problem, then surely making the UFH the last return won't make the situation any worse?

Sadly, that was what I meant.

Usually the flow goes into the top of the cylinder coil and the cooler return comes out of the bottom of the coil. That is conventional, but there is a minority school of thought that it is better to go into the bottom, hence my interest.

If you are suggesting you don't know where the radiator circuit and cylinder coil circuit join, however, then bear in mind what Shaun and others are saying about the 'three tees rule'. What I've said previously is based on your diagram being correct.

It is.

No, I was thinking a fixed bypass really such as a gate or a globe valve as the return from the UFH will be much cooler than that from the radiators once the system is warm and I would want to prevent condensation occurring inside the boiler if the boiler is not a condensing boiler, and the potential of weird behaviour if the boiler is a condensing boiler but may respond to an unusually cool return in an undesirable way.

Thanks for this,

OK so flow going up to being after the current pump, thanks for clarifying (painful as it will be)

Yes the cylinder does go hot in high, return (cold) at the bottom, my diagram is wrong, sorry

In terms of the order of the of the returns I think it goes Cylinder, rads then definitely UFH. I have attached some photos so you can see what I can see.

"fixed bypass really such as a gate or a globe valve" ok I see what your saying, I'll make a note of that for when someone is able to come and sort this.

Thanks again for your wisdom!

Ric2013 · Dec 14, 2021

ejkilby1 said:
"fixed bypass really such as a gate or a globe valve" ok I see what your saying, I'll make a note of that for when someone is able to come and sort this.

Take the advice of whoever actually is there to see your system over me replying from a distance, but you can always throw the idea out there, and if you fit the bypass and it proves to be unneccessary you can always close it.

UFH not getting hot on vented system

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