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.

 

[stevetheplumber]

sounds like you need some balancing valves is the basement manifold of the same feed as the cylinder ? have you tried it with that manifold isolated

 

[Chalked]

If a low loss header was fitted, why wasn't the cylinder piped back to this with its own circulator ? This would have cured it .

 

[bennygas]

No heating of cylinder when underfloor is on? Just an idea, but is the flow temp from the boiler staying high even with all the underfloor calling? The only reason I say this is that I've had a situation like this in the past, and found that if the return coming back from the underfloor is very cold and the boiler can't put enough heat into the water in one pass to raise it to the temperature required for hot water preparation then it can cause similar symptoms. Checked volume/mass flow rate through the boiler and had a look at what the flow and return temps are doing? this doesn't answer the hot water cycling issue though.I guess if this was the case, the solution would be to implement some form of hot water priority set up. Like I say, just an idea.

 

[bennygas]

Is this when someone curses the apprentice who left a gate valve 90% shut....

 

[Carrera]

Thanks for the replies so far, responses:

Stevetheplumber
Basement manifold is off the same feed as the cylinder
if I isolate the basement manifold and just run that, hot water and basement heating work together, as soon as I switch the rest on I loose the hot water cylinder and basement manifold

Chalked
re the low Loss header and and circ back, I will talk to the plumber

Bennygas
re temp being very on return, even if one manifold is running, ie low heat call I still get nothing flowing through the cylinder

 

[Centralheatking]

Hi Carrera -

Welcome to UKPF - you in the right ball park for help - I have read your post
carefully and have some observations and questions.

1. Do you own a porsche motor car - if which model
2.the specifcation you present of your c/h system is top dollar - it has been well designed

so- I think the problem is in the fitting or most likely a component - as it is so new
can you get the installer back ? - my outfit would rtn to problem like this even if is
beyond our promise

3. To help us can you post a diagram of your set up then we can all have a look

Centralheatking

 

[Carrera]

Hi centralheatking,
1 don't own a porsche I wish I did, but all funds have gone into self build.
the installer designed the system,Manx they are in trying to sort it out but going round in circles trying things. I thought I would try and get some fresh views to help as I have to switch between heating and hot water manually at the moment, not what I was expecting.
i will try and put a drawing together of the plant room, but may be easier to take a picture and post it with some annotations. Would that help?
Regards

 

[Gray0689]

Yes a sketch of your system be good

 

[chris watkins]

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.

Has there ever been more than one pump on the system ??
You say the original one was upgrades to the Magna but for a LL system to work there must be a constant flow rate through the boiler (as required by the boiler manufacturer) so a dedicated circulator would be required for this & than as a minimum a circulator for the HWS primaries & one for the heating.
Without the required flow rate the temp at the boiler quickly rises & it modulates down.

 

[Carrera]

Has there ever been more than one pump on the system ??
You say the original one was upgrades to the Magna but for a LL system to work there must be a constant flow rate through the boiler (as required by the boiler manufacturer) so a dedicated circulator would be required for this & than as a minimum a circulator for the HWS primaries & one for the heating.
Without the required flow rate the temp at the boiler quickly rises & it modulates down.

Originally one pump, then LL SYSTEM had 3 pumps, one circulating, one feeding heating demand, and one trying to pump round the cylinder (unsuccessful), now back to one pump but a bigger one

 

[Carrera]

I thought would be easier to put in a picture of the plant room rather than a sketch, but having trouble up loading it using the insert picture button. is there a trick to it?

 

[jase158]

I would suggest electrical fault, sounds like the hot water circuit isn't opening when the rest is open. If it all works individually then it is all working but not as it should, either this or a balancing issue. My guess would be an electrical fault though. Possibly one of the 2 port valves not wired correctly

 

[Ermintrude]

If you get ufh up to temp I .e house is at 25 c then lower set points on ufh with cylinder in demand and cyl should heat up if electrical system in correctly. Sounds more like the return from one of the blended returns ( ufh) is running through cylinder ? Balancing / hydraulic issue.

Which cylinder cold switch on hw load . Run until flow is hot , ( run off hot water to ensure demand in cylinder is constant)
Turn on one manifold at a time and wait until the return is at a constant temp, keep working through until you switch one on and cyl flow goes cold. Then you know which one is the prob.

 

[Centralheatking]

Diagram - CHK

 

[Howsie]

Get a decent plumber in.

 

[Ermintrude]

Get a decent plumber in.

You got number for a company who use A team theme tune ? Sure they have this on roughbooks?

 

[Carrera]

Diagram - CHK

I am having trouble uploading a picture of the layout, anyone help?

 

[Carrera]

Don it albeit sideways!
this is the plant room setup

 

[Chalked]

Presumed the cylinder was miles away.! Problem that sticks out to me is why is there a tee off before the pump?
pressure vessel?
another pump? Noooo

 

[Gray0689]

View attachment 16396
Don it albeit sideways!
this is the plant room setup

For the size of house all looks very small !

 

[Ermintrude]

Is that a two or 3 port on cyl? Where do the pipes at bottom on pic disappear to?
Yes the tee under the boiler behind pump also interesting? What's the total load on the heating system as it looks to be 28 and 22 mm

 

[Chalked]

The house has underfloor throughout so output may be ok.
I personally think wb heat exchangers are too restrictive.
a house of this size would have been better served with two smaller boilers on a low loss header. As underfloor does not need a lot of kw, but needs a good flow rate.

 

[Chalked]

Is that a two or 3 port on cyl? Where do the pipes at bottom on pic disappear to?
Yes the tee under the boiler behind pump also interesting? What's the total load on the heating system as it looks to be 28 and 22 mm

Zooming in its a zone valve.

 

[Gray0689]

The house has underfloor throughout so output may be ok.
I personally think wb heat exchangers are too restrictive.
a house of this size would have been better served with two smaller boilers on a low loss header. As underfloor does not need a lot of kw, but needs a good flow rate.

6500sqfoot house
6 manifolds 500litre unvented cylinder
Inch pipe all to small for my liking