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]

My understanding is the UFH pumps only circulate the blended water in the circuits, there is a clear path through from flow to return and the UFH only takes primary flow water to make up the lost heat in the circuit. The flow and return to manifold will need balancing to 20 degree differential once the whole system can be run.

as it is they are probably not balanced and the return temp is being prematurely raised which will cause the boiler to cycle.

The hw is not working due to a very low resistance circuit (much lower than cylinder circuit) maybe as described above, or if what carrera is saying is true, reverse circulation through the cylinder.

the magna is the main pump and when you consider what it's doing, should be man enough. The Pipework should be up to the job if I understand the design.

My advise would be to tee in the hot water return independently to ensure it's not reverse circulating, double check everything in that circuit and the Pipework for blockage.

the boiler connections are 28mm and the internals are probably 22mm, it's the overall resistance not one small section of pipe that will probably be negligible.

 

[Carrera]

Looks to me 6 manifolds 3flows 3 returns and flow return to rad circuit

Do you have the sheet with the calcs for the underfloor Spec manifold sizes pipe length ect

Yes , you might be able to get one more with a bit of fiddling

You would end up with 3 manifolds on one circuit, and 3 independent manifolds, so four feeds

 

[Gray0689]

Yes , you might be able to get one more with a bit of fiddling

You would end up with 3 manifolds on one circuit, and 3 independent manifolds, so four feeds

What size are the manifolds on the one line of 28mm flow
How many ports on manifolds

 

[Gray0689]

My understanding is the UFH pumps only circulate the blended water in the circuits, there is a clear path through from flow to return and the UFH only takes primary flow water to make up the lost heat in the circuit. The flow and return to manifold will need balancing to 20 degree differential once the whole system can be run.

as it is they are probably not balanced and the return temp is being prematurely raised which will cause the boiler to cycle.

The hw is not working due to a very low resistance circuit (much lower than cylinder circuit) maybe as described above, or if what carrera is saying is true, reverse circulation through the cylinder.

the magna is the main pump and when you consider what it's doing, should be man enough. The Pipework should be up to the job if I understand the design.

My advise would be to tee in the hot water return independently to ensure it's not reverse circulating, double check everything in that circuit and the Pipework for blockage.

the boiler connections are 28mm and the internals are probably 22mm, it's the overall resistance not one small section of pipe that will probably be negligible.

The blended water will be the full flow if the boiler can't heat the demand on the heating
6 manifolds 6 pumps going on a flow out of boiler at 28mm don't matter if some of pipework is 35mm won't get the flow rate out it needs that's my opinion anyway

 

[Nostrum]

So your telling me that Pipework won't be able to cope with 6k of heat (min output fully modulated approx)?

Of course it will. But not if it's coming back at almost full temperature, it'll cycle.

the problem is to much flow, not to little.

 

[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.