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.

 

[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.

 

[Nostrum]

Carrera, the flow to hot water cylinder valve tees off the main run as it were, then before it gets to the hot water zone valve it tees off again, what's that for?

this is a Pipework issue, I'm sure of it, somewhere in that plant room, maybe with a combination of balancing chucked in as well.

 

[mark_mc]

NOT WORKING

undersized / designed wrong / needed re-done/

 

[Nostrum]

NOT WORKING

undersized / designed wrong / needed re-done/

very helpful. If it were undersized Pipework the cylinder would be robbing all the heat as the resistance to UFH would be too high.

 

[Nostrum]

And putting the smaller pump back in and it still working the same as it was is proof of that.

 

[mark_mc]

Its getting to ufh circuits but i bet its getting there great.
look at the resistance str after the pump you have the t's for the cylinder and which way would the water rather go-- to the ufh
and then you have the t's of to the flow return to the basement ufh manifold
to much resistance - no thinking in what way the water would behave
if you where honest looking at that pic you would never install it that way, its just wrong.
if it was pumped independently everything would work



i always price so that it works with zero defects and that comes with a extra cost.