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.

 

[Gray0689]

???

1600 square feet = 149 square metres.

Or am I misunderstanding you?

House is 6500 square foot ray
500litre cylinder
6 manifolds
7 towel rads

 

[Ray Stafford]

House is 6500 square foot ray
500litre cylinder
6 manifolds
7 towel rads

Gotcha. So original 1600 should have said 6500? Makes sense now. Ta

<memo to self - read the whole thread>

 

[Gray0689]

A low loss header would of been good for that set up
But to be honest I would be thinking the plumber made a hash of that as pipework is undersized
Another good job ruined by cutting corners imho

 

[Ermintrude]

A low loss header would of been good for that set up
But to be honest I would be thinking the plumber made a hash of that as pipework is undersized
Another good job ruined by cutting corners imho

Boiler is a 1/3 of the size it should be ? 604m2 @0.150kw/m2 = 90kw just for the floors! 90kw ain't ever fitting down 28mm unless it's running at 140m/s

 

[Ray Stafford]

Heat loss calcis have been done to size the boiler to the heat output required, indicating the boiler is oversized by about

Any chance of seeing those calcs?

 

[Carrera]

let me try and answer some of the questions, btw the plumber is here at the moment!
Heat loss calcs indicate heating requirement is 27 kW, done prior to boiler selection due to level of insulation, airtightness and mechanical ventilation and heat recovery systems in place.

pipes disappearing down off the picture are flow and return to the basement manifold which sits about 6 feet away

pipework is 28mm most of the way round the house to the manifolds, changing to 22 on the top floor

Flow through hot water cylinder not working even if only one manifold is running, ie extremely low heating load.

The screed on the for is the anhydrite liquid screed, which transfers heat a lot quicker than normal and is only 50 mm thick

the T referred to behind the pump? There is no t behind the pump, the one to the right is flow out, one on the left is just an elbow leading to a T to the cylinder, followed by a T to the basement manifold

 

[Chalked]

Are my eyes deceiving me? I can definitely see two pipes coming down from the boiler, both with tees?
these go off before the pump.

 

[diamondgas]

Without checking for none return valves etc I'd say your problem could be caused by the tee before the pump, unless there's a none-return valve down stream and another pump?

Already mentioned previously, by-the-way !

 

[diamondgas]

The circled bit...

 

[Carrera]

Ok I see, the two Ts one on flow and one on return leads to manual dead ends that are used to drain system, just a bit beyond the picture, and below that is the system filling loop

 

[Ermintrude]

44kw/m2 you should have ashp or gshp!

 

[Ermintrude]

So have u tried bringing one zone in at a time when sys hot and DHW cylinder is cold? Looks like a pretty messy set up. Was this plumbers first job like this?

 

[Carrera]

So have u tried bringing one zone in at a time when sys hot and DHW cylinder is cold? Looks like a pretty messy set up. Was this plumbers first job like this?

They do houses this size all the time, and say they haven't had this issue crop up before. I have had the same guy, their senior guy, from first fix to final and they have a good reputation.

re bringing hot water online with the system hot and one zone at a time, can you confirm whether you mean one zone or complete manifold?

 

[Gray0689]

So have u tried bringing one zone in at a time when sys hot and DHW cylinder is cold? Looks like a pretty messy set up. Was this plumbers first job like this?

I agree looks like he didn't fully understand what he was going is he new to plumbing large houses looks like it to be honest
I take it hasn't got building control cert yet as not even a bit of lagging
What is your area there maybe a member on here to come and maybe sort you out depending on how the pipework has been left from pic it don't look to tasty to be honest
But that's just my option
Please tell your plumber to join and we can discuss this further

 

[diamondgas]

Ok I see, the two Ts one on flow and one on return leads to manual dead ends that are used to drain system, just a bit beyond the picture, and below that is the system filling loop

Well if that's the case then the water should wizz around the hot water circuit when it's on and, if anything, bi-pass the UFH circuits IMO ... Water will take its easiest route to complete a circuit

Is that some sort of balancing valve fitted on the return from the cylinder? Is it fully open? Not that it should be, however it's a possibility that it's giving you grief... Otherwise, as mentioned previously, a wiring issue potentially? I don't see any separate zone valves on the individual UFH heating circuits. Are they remote from the 'plant'?

Regards wiring, easy check is that the hot water zone valve is staying open when the heating is on.

I'd bet this was a pig to balance? Also an issue mentioned previously!

Other possibilities could be a faulty/restricted hot water valve, and or hot water circuit! I think that's also been mentioned? However trying to keep up with all that have posted can be difficult I guess, I am? Pump could be an issue? I really am not a fan of the new boys! Could even have a dodgy boiler that's restricting flow?

If your plumbers pulling his hair out then a great indicator of flow issues is temperature difference primary flow and return! I think, if they haven't already done so, I'd be checking each individual circuit to see what they're giving. Any huge difference can help diagnose circulation issues... IMHO

 

[Chalked]

I think some here are been a little harsh, but back to the subject.

If its the underfloor heating that is messing with the hot water. Have you tried turning each manifold off and let the towel rail and water heat up on their own.

is it possible to post a picture of one of the manifolds to see how they are connected?

 

[Chalked]

Had another thought.
I should be flowing like a good un around the coil, but looking at the picture, could it simply be one of the male threaded fitting that are made into the cylinder having a film of ptfe over the face.
trust me I've seen it a few times.

 

[Gray0689]

I think some here are been a little harsh, but back to the subject.

If its the underfloor heating that is messing with the hot water. Have you tried turning each manifold off and let the towel rail and water heat up on their own.

is it possible to post a picture of one of the manifolds to see how they are connected?

Would you want a £30k to £40k job to look like that!!!!!

 

[Chalked]

Would you want a £30k to £40k job to look like that!!!!!

No mate .:boxing_smiley:
but aren't we trying to get to the root of the problem. Not weather it's lagged !:wink:

 

[Gray0689]

No mate .:boxing_smiley:
but aren't we trying to get to the root of the problem. Not weather it's lagged !:wink:

I don't think it ever going to be right the way it's piped up anyway
It's 6500square foot house over 4 floors probably numerous bathrooms/en suits
I don't see a secondary return pump a 500 litre cylinder
I see one grundfos magna 25-80 doing everything 6manifolds and rad circuit highest bore of pipe 28mm in boiler house a single boiler with no back up
Where going in to light commercial here this is very basic
I don't know full story so it be good if the plumber was on to say his bit as he may of been instructed to do it very cheap as that's the way it's looking

If it was done with a simple header with separate feeds at least the cause be a lot simpler to see and sort out
It should be a simple fix as the cylinder right next to boiler

But will it ever be a great system I don't thing so it will probably work but

 

[diamondgas]

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.

Just re-read your post and find this strange! It doesn't go through the 'T' to the hot water when the heating is on ... the way it's piped it should pi$$ through the hot water circuit ... I'd concentrate on the hot water circuit, from what you've said! The fact that it "heats up" is incidental as it will if its the only thing on! However if the flow through the circuit is restricted then it'll be bi-passed, virtually, when everything else is calling! IMO

 

[Carrera]

I will try and answer some of the points.
Area is south bucks, I would happily pay someone to look and advise me, as I would like to give the plumber the opportunity to put right, and they are trying!

there is a bronze pump for secondary hot water return, just not in the picture it's above the cylinder.

One of the upstairs manifolds sideways!View attachment 16405

Not signed off by building control as the rest is not finished, however we have been living in the house for just under a year, heating was working fine, just not in tandem with the hot water

For the time being the magna pump has been removed and replaced with the old pump, as it isn't working properly, as they are also trying to overcome a flow issue introduced with the recent messing around

Also the non return valve on the flow out from the cylinder has been removed to reduce resistance, however, what is happening now is if the heating is on and the water is switched on, the flow is being pulled backward through the cylinder and cooling the flow up to the heating

 

[Ermintrude]

They do houses this size all the time, and say they haven't had this issue crop up before. I have had the same guy, their senior guy, from first fix to final and they have a good reputation.

re bringing hot water online with the system hot and one zone at a time, can you confirm whether you mean one zone or complete manifold?

Pull one manifold at a time

 

[Carrera]

Just re-read your post and find this strange! It doesn't go through the 'T' to the hot water when the heating is on ... the way it's piped it should pi$$ through the hot water circuit ... I'd concentrate on the hot water circuit, from what you've said! The fact that it "heats up" is incidental as it will if its the only thing on! However if the flow through the circuit is restricted then it'll be bi-passed, virtually, when everything else is calling! IMO

thats precisely the piece that's baffling the plumber and he has been concentrating on the resistance aspect.

 

[Gray0689]

Just re-read your post and find this strange! It doesn't go through the 'T' to the hot water when the heating is on ... the way it's piped it should pi$$ through the hot water circuit ... I'd concentrate on the hot water circuit, from what you've said! The fact that it "heats up" is incidental as it will if its the only thing on! However if the flow through the circuit is restricted then it'll be bi-passed, virtually, when everything else is calling! IMO

From what I can see of pipework if the umber on site can't see how it not a simple fix the cylinder Is a metre away can't be that many things

 

[Gray0689]

thats precisely the piece that's baffling the plumber and he has been concentrating on the resistance aspect.

What exactly has he tried
Has he checked pump is running when on hot water only
Has he checked pump running on heating and hot water
Has he checked the 2 port is opening when the above Is on
Has the electrical side of things been checked

 

[diamondgas]

thats precisely the piece that's baffling the plumber and he has been concentrating on the resistance aspect.

Temp difference between F&R on hot water only? ... There may be something within the coil of the cylinder itself or , as mentioned, a man made restriction on installation ... PTFE across the pipe opening? A temp check of the flow through the cylinder will quickly tell you whether or not you have a restricted flow. It's then a strip down to find out where it is I'd imagine

 

[Gray0689]

Your always going to have a flow problem imho as the massive load you will be trying to get out of that 28mm pipe to flow to 6manifolds for that size of a house is just silly

 

[Carrera]

What exactly has he tried
Has he checked pump is running when on hot water only
Has he checked pump running on heating and hot water
Has he checked the 2 port is opening when the above Is on
Has the electrical side of things been checked

All of the above have been checked and checked again

 

[Gray0689]

Did he try blowing out the coil with mains