Underfloor heating not getting hot enough

Vicdiy · Jan 31, 2023

My daughter has just had a new boiler, her system is radiators to upper floors and underfloor to all of ground floor. Despite the valve serving the underfloor being turned up to a high temperature and the pipe leading to the pump being very hot the flow and return pipes on the manifold are only luke warm. The valve is on 60 or 65 but the temperature on the dial after the pump is only 30 degrees. I enclose a photo with the flow and return marked in yellow and the hot pipe leading to the pump marked in blue. The pump sounds as if it is working ok. In addition I can’t see how the flow on each circuit can be adjusted as the flow indicators do not look like they can be adjusted but there has to be a way.
Any advice would be much appreciated

gmartine · Jan 31, 2023

Did the system work with the old boiler? Can you upload a picture of the new boiler with surrounding pipework.

ShaunCorbs · Jan 31, 2023

Also you shouldn’t have the ufh system running at 60 dc what was it designed at ?

There’s flow going through them and adjusting them won’t fix the problem as there pumping / flowing best to stop adjusting things and find what the actual problem is before you break something

Vicdiy · Jan 31, 2023

ShaunCorbs said:
Also you shouldn’t have the ufh system running at 60 dc what was it designed at ?

There’s flow going through them and adjusting them won’t fix the problem as there pumping / flowing best to stop adjusting things and find what the actual problem is before you break something

I haven’t done anything. The engineer that installed the new boiler said to turn up to 60 for a while as the underfloor wasn’t getting very warm so my daughter did what he said. I haven’t adjusted anything, my question about how to adjust the flow was just out of interest, I just try to advise/ help when I can but I will not be touching it, I will leave that to the experts.

Vicdiy · Jan 31, 2023

Vicdiy said:
I haven’t done anything. The engineer that installed the new boiler said to turn up to 60 for a while as the underfloor wasn’t getting very warm so my daughter did what he said. I haven’t adjusted anything, my question about how to adjust the flow was just out of interest, I just try to advise/ help when I can but I will not be touching it, I will leave that to the experts.

ShaunCorbs · Jan 31, 2023

Vicdiy said:
I haven’t done anything. The engineer that installed the new boiler said to turn up to 60 for a while as the underfloor wasn’t getting very warm so my daughter did what he said. I haven’t adjusted anything, my question about how to adjust the flow was just out of interest, I just try to advise/ help when I can but I will not be touching it, I will leave that to the experts.

Well that’s bad advice from him high temp can cause the floor to crack / warp / do some decent damage did he flush the loops as he’s drained down ?

The flow is set to spec so should need adjusting

Vicdiy · Jan 31, 2023

gmartine said:
Did the system work with the old boiler? Can you upload a picture of the new boiler with surrounding pipework.

Yes it did work with the old boiler which was a Remeha 45KW . The heating was off for nearly two weeks while getting a new one installed was all sorted. The enclosed photo is of the low loss header below the old boiler, that is still there. The new boiler is Worcester Bosch regular boiler, sorry no photo as daughter lives on other side of Leeds.

Vicdiy · Jan 31, 2023

ShaunCorbs said:
Well that’s bad advice from him high temp can cause the floor to crack / warp / do some decent damage did he flush the loops as he’s drained down ?

The flow is set to spec so should need adjusting

I will tell her to turn it down. You say the flow is set to spec so should need adjusting, did you mean to say shouldn’t need adjusting ?

SimonG · Feb 1, 2023

Could be air locked. Need mains on and flush through each loop.

Vicdiy · Feb 1, 2023

SimonG said:
Could be air locked. Need mains on and flush through each loop.

Yes, it could be. The problem they have is the contract with Corgi who kindly replaced the boiler and separate pump does not cover the underfloor heating. The engineer who replaced the boiler is just trying to get it running like before but I doubt that he would flush through each loop.
How are the flow rates on each loop adjusted ? as the flow indicators do not look as if they have any adjustment. I have seen a few videos on YouTube where they simply adjust the flow indicator but that doesn’t look possible on their system

Vicdiy · Feb 1, 2023

I’ve been to my daughter’s again this morning and taken a few more pics and felt the temperature of the flow and return on the underfloor heating manifold. The 15 mm supply pipe is very hot until it joins the valve arrowed yellow which links with the return flow on the manifold after that it is only lukewarm and the temperature gauge shows around 28 degrees. I am not a heating engineer but is this a mixing valve and would turning the nut increase the ratio of new hot water to the return water from the manifold ? Her floors are definitely warmer but not as warm as they should be which makes sense if the water flowing from the manifold is not hot enough.

Vicdiy · Feb 1, 2023

Vicdiy said:
Yes it did work with the old boiler which was a Remeha 45KW . The heating was off for nearly two weeks while getting a new one installed was all sorted. The enclosed photo is of the low loss header below the old boiler, that is still there. The new boiler is Worcester Bosch regular boiler, sorry no photo as daughter lives on other side of Leeds.

More pics of the installation after new boiler. I have posted separately asking if the valve arrowed yellow is a mixing valve and if adjusting this would increase the temperature of the water flowing through the manifold. Is it just a matter of turning the nut and which way would make it hotter?

Ben-gee · Feb 1, 2023

Stop mucking about , get the installer back- or another competent plumber who knows what they’re looking at.

Vicdiy · Feb 1, 2023

Ben-gee said:
Stop mucking about , get the installer back- or another competent plumber who knows what they’re looking at.

I agree, I am not mucking about just trying to give a bit of advice but not touching anything. It is not entirely straightforward as Corgi have replaced the boiler as the original Remeha was condemned and it was only eight years old but they don’t cover underfloor heating systems. The new installer has got the system running with new Worcester Bosch boiler but the underfloor is not as warm as it should be, he is trying to work out why but strictly speaking they are not responsible for the underfloor part. They may have to get somebody else back if he has no luck tomorrow

Ben-gee · Feb 1, 2023

That’s what I mean, you need someone who knows what they are looking at not someone who can just chuck a boiler on the wall - if it works fine, if it doesn’t they haven’t got a clue.

John.g · Feb 2, 2023

Vicdiy said:
More pics of the installation after new boiler. I have posted separately asking if the valve arrowed yellow is a mixing valve and if adjusting this would increase the temperature of the water flowing through the manifold. Is it just a matter of turning the nut and which way would make it hotter?View attachment 81264 View attachment 81265 View attachment 81266 View attachment 81267 View attachment 81268

Can you take the 4 LLH temperatures with a thermal gun or the like you may be able to get the boiler flow and return temps from the boiler itself, also any displayed tempsfrom the UFH manifolds, takeany temps with rads only on, UFH only on and with both RADS&UFH on.

Vicdiy · Feb 2, 2023

John.g said:
Can you take the 4 LLH temperatures with a thermal gun or the like you may be able to get the boiler flow and return temps from the boiler itself, also any displayed tempsfrom the UFH manifolds, takeany temps with rads only on, UFH only on and with both RADS&UFH on.

The boiler flow and returns are fine, all the radiators are fine. The flow pipe from the boiler to the UFH is fine but after it links with the return from the UFH it is only lukewarm, this then goes through the pump and back into the flow manifold to the UFH. It seems to me that there is too much of the return water and not enough of the new hot flow from the boiler when they are mixed but how can that be adjusted. The new boiler installer simply turned the thermostatic valve up to 60 degrees but that didn’t make any difference, still lukewarm water circulating through the UFH.

John.g · Feb 3, 2023

If you had a 5kw UFH demand with flow/return of 45C/37C from a boiler flow temp of 65C then a hot flow of 3.59LPM at 65C mixed with 5.36LPM of UFH return water at 37C is required to give a UFH flow of 8.95LPM with a dT of 8C &5kw.
You may require separate pumps on rads and UFH if both fed from the LLH.
Does the UFH perform OK on its own?

Vicdiy · Feb 4, 2023

John.g said:
Can you take the 4 LLH temperatures with a thermal gun or the like you may be able to get the boiler flow and return temps from the boiler itself, also any displayed tempsfrom the UFH manifolds, takeany temps with rads only on, UFH only on and with both RADS&UFH on.

John.g said:
If you had a 5kw UFH demand with flow/return of 45C/37C from a boiler flow temp of 65C then a hot flow of 3.59LPM at 65C mixed with 5.36LPM of UFH return water at 37C is required to give a UFH flow of 8.95LPM with a dT of 8C &5kw.
You may require separate pumps on rads and UFH if both fed from the LLH.
Does the UFH perform OK on its own?

There are separate pumps to rads, UFH and also to the hot water. The UFH doesn’t perform Ok on its own it isn’t terrible it just doesn’t get very warm. As I said before the supply to it is hot but just not hot enough once it mixes with the return flow.

John.g · Feb 4, 2023

Assuming the UFH TMV is working correctly it still requires ~ 10C/15C differential to operate properly so possibly the LLH secondary flow is excessively higher than the primary flow which means the UFH return will just short circuit the excess to the flow side.

Vicdiy · Feb 5, 2023

John.g said:
Assuming the UFH TMV is working correctly it still requires ~ 10C/15C differential to operate properly so possibly the LLH secondary flow is excessively higher than the primary flow which means the UFH return will just short circuit the excess to the flow side.

Good point. My daughter rang me yesterday and said that following the latest visit from the boiler installer to tidy up some electrics the UFH was now working perfectly. Unfortunately she wasn’t there at the time but is texting him to see if he had done anything to the UFH circuit as he had previously said he didn’t know why it wasn’t hot enough. I will post if I find anything out. Thanks for your advice.

Underfloor heating not getting hot enough

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