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.

 

[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

 

[Ermintrude]

Did he try blowing out the coil with mains

Surely that will blow the mains fuse? 100a through coil?????? Oh water right !

Close all your valves to zones and boiler so only route from loop to drain off is the coil , open filling loop and drain off , open and close drain off to allow pressure to build and remove any bits?? No sawdust or plaster board ore even air in coil??

 

[Carrera]

Did he try blowing out the coil with mains

yes that was done today

 

[mark_mc]

have to agree with gray on this
everything is undersized
if all the circuits go back to the plant room you may be able to solve with a low loss header and pump to each manifold with separate pump
hot water return may be impossible without taking up floors
but would really look at pumping each manifold if possible, and it looks like 22mm doing the manifold in pic which i would be bring 28mm too, better looking at it than looking for it.

 

[Nostrum]

It looks like it could be reverse circulation does the flow/return that lead to the basement have a balancing valve on?

From the picture ( which is very hard to make out on an ipad) flow could be being forced down to the basement circuit then back through the coil and into the flow again which is then leading up to the UFH circuit which would add up with what your saying. A bit like a 1 pipe system.

How I haven't quite figured out yet, are you sure that valve is opening fully?

 

[Nostrum]

Is some of that Pipework 35mm?

 

[Carrera]

It looks like it could be reverse circulation does the flow/return that lead to the basement have a balancing valve on?

From the picture ( which is very hard to make out on an ipad) flow could be being forced down to the basement circuit then back through the coil and into the flow again which is then leading up to the UFH circuit which would add up with what your saying. A bit like a 1 pipe system.

How I haven't quite figured out yet, are you sure that valve is opening fully?

valve is definitely opening up properly
some pope work in the basement is greater that 28mm

 

[Gray0689]

valve is definitely opening up properly
some pope work in the basement is greater that 28mm

The flow return from boiler is 28mm

 

[Nostrum]

Yeah if you look at the right hand side 'manifold' 2 are 28mm up to the UFH and the one on the far right is 22mm, there is a reducer before hey tee so it must be 35mm, it then reduces on the tee under the boiler, so flow out of boiler is 28mm into a 35mm tee. That why the pump doesn't have standard valves.

If you isolate the basement manifold does your cylinder stop reverse circulating?

 

[stevetheplumber]

all looks well undersized to me

 

[Carrera]

Yeah if you look at the right hand side 'manifold' 2 are 28mm up to the UFH and the one on the far right is 22mm, there is a reducer before hey tee so it must be 35mm, it then reduces on the tee under the boiler, so flow out of boiler is 28mm into a 35mm tee. That why the pump doesn't have standard valves.

If you isolate the basement manifold does your cylinder stop reverse circulating?

Will have to test tomorrow and get back to you

 

[Ermintrude]

Can I come and fix it for u? I'm reasonable and will get it working 100%

Not cheap not by a long way one 3k plus materials

 

[mark_mc]

we are all hitting are head against a brick wall, as we can all agree the install is undersized and that we would all have done it another way.
its now at the point it seems that the poor plumber that put it know that to.
its undersized a large cylinder requires independent 28mm flow and return in most cases.

 

[Gray0689]

Will have to test tomorrow and get back to you

Tell you plumber you make you out a sketch of the pipe work then we will be able to get a better look
Who specced the job for that kind of size I'd like to think there was a me consultation in design

 

[Ermintrude]

Tell you plumber you make you out a sketch of the pipe work then we will be able to get a better look
Who specced the job for that kind of size I'd like to think there was a me consultation in design

Nope but his mate knows all about boilers n stuff

 

[Nostrum]

Guys, look at the picture, this isn't undersized, its 35mm and 28mm. The picture is deceiving but it is larger Pipework than you think.