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]

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.

 

[Gray0689]

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.

It's undersized it needs a low loss header and re piped properly
As already said big drop at flow meters is a big giveaway

 

[Carrera]

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.

That next T leads to the small basement manifold which is also located in the plant room

 

[Gray0689]

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

The manifolds are pumped the magna is acting as a shunt pump
It can't get enough flow through that 28mm IMO

 

[Nostrum]

Yes I agree I wouldn't have installed it anything like that and agree with you, always fit it right the first time dare than go back replacing the corners you have cut.

but just saying rip it out and start again is not a great help, and this fault is due to a different fault IMO.

He reality is no one really knows how well it's going to work once sorted, but when you are as balls deep as this now, it's worth trying to rectify before chucking the towel in completely. It's not the O.P's fault, whatever the price someone has been contracted to carry out this work. If they are confident they can get it running with this design then give them the benefit of the doubt.

if the O.P decides once/if it is running that it's not good enough, that is the time to question the design.

Whilst it's not our job to rectify, the post is asking for advice.

Its one of the more interesting posts anyway!

 

[Gray0689]

That next T leads to the small basement manifold which is also located in the plant room

I know it's not what you want to hear mate but we are just trying to help where not just slating your plumbers work you have a problem I'm sure you paid big money for this job

Plumbing is a funny thing it could be plumbed crap but it can work as far as the customer is concerned as long as he turns the heAt on he gets heat it's grand but unfortunately that's not the case
For a smaller house your set up probably be grand but not a house that size
It really should of been designed by a M&E consultant with spec they would not do it that way I can guarantee that

 

[Nostrum]

The manifolds are pumped the magna is acting as a shunt pump
It can't get enough flow through that 28mm IMO

are you sure, where's the pump for the cylinder , the bypass circuit and why is the pump wired directly to the boiler?

 

[Gray0689]

Yes I agree I wouldn't have installed it anything like that and agree with you, always fit it right the first time dare than go back replacing the corners you have cut.

but just saying rip it out and start again is not a great help, and this fault is due to a different fault IMO.

He reality is no one really knows how well it's going to work once sorted, but when you are as balls deep as this now, it's worth trying to rectify before chucking the towel in completely. It's not the O.P's fault, whatever the price someone has been contracted to carry out this work. If they are confident they can get it running with this design then give them the benefit of the doubt.

if the O.P decides once/if it is running that it's not good enough, that is the time to question the design.

Whilst it's not our job to rectify, the post is asking for advice.

Its one of the more interesting posts anyway!

Looking at a bad picture of half an installation don't think where going to see the full picture
Yes he ha asked for advice and I do believe he has had good advice
The bet seems to have checked all the normal causes that it could be so now need to look at it deeper
As all were doing is just guessing now but as almost everyone has stated already it looks undersized

 

[Gray0689]

are you sure, where's the pump for the cylinder , the bypass circuit and why is the pump wired directly to the boiler?

The magna is the pump for cylinder
Ps I'm not an electricians ask me one I know lol

 

[Nostrum]

Well, maybe that's where we disagree, looks like 35mm and 28mm UFH circuits with 22mm towel rail circuit to me. Can't be sure but the hw circuit looks like it could be 28mm as well.

 

[Gray0689]

Well, maybe that's where we disagree, looks like 35mm and 28mm UFH circuits with 22mm towel rail circuit to me. Can't be sure but the hw circuit looks like it could be 28mm as well.

Yes there is some 35mm but coming off 28mm from boiler the 35mm is useless

 

[Gray0689]

Well, maybe that's where we disagree, looks like 35mm and 28mm UFH circuits with 22mm towel rail circuit to me. Can't be sure but the hw circuit looks like it could be 28mm as well.

To me when the underfloor and hot water on together
The flow that all them manifolds need and don't forget 6 pumps going and a shunt pump there starving the hot water coil the wY it's plumbed


As has been said a few times if you was to shut down manifolds one at a time eventually you will get the heating and hot water going
But needs re plumbed

 

[Carrera]

I welcome all the input, I am not trying to defend or slate the plumber. I am just trying to get to a working system. I am not wedded to this or any other design.

Yes I paid a lot for the install, wasn't the cheapest quote, but these guys do 6 or 7 houses this size or similar and came recommended.

design was left to them, as it is on most of there jobs.

ripping up floors is not an option, ufh pipes are in.

ripping down ceilings is something I don't really want to do, and without doing this I cannot plumb the manifolds back separately

i am just getting slated at the monument by the wife and kids every time the hot water isn't hot!

 

[mark_mc]

put the immersion on, and enjoy christmas.

it will get sorted with the help from this forum

 

[Carrera]

Even with only one manifold going the hot water doe not work with the heating

 

[Carrera]

put the immersion on, and enjoy christmas.

it will get sorted with the help from this forum

6kw immersion does nothing to a 500 litre cylinder!

 

[mark_mc]

crap.

 

[Gray0689]

To me the only way to do this now

1 put in a low loss header and re pipe the boiler room
Separate feeds to the underfloor pipework you have in place
Separate feeds to rad circuit
And separate to cylinder
All with there own pumps there letting them work on there own

Or if you have the room I'd put in a buffer tank
And pipe from buffer


It's hard for you I understand as your the one who gets the grief at home and then listening to advice here I'm the worst for making it sound like I'm just slating the plumber not the best at making posts sound nice and friendly but
I don't blame the boy on site as he probably been told to do it that way
And on a smaller house probably be no problem at all

 

[mark_mc]

how many circuits can we divid the system into as it sits without lifting floorboards/causing too much damage

 

[Gray0689]

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

 

[mark_mc]

buffer would be a good idea.
only gas at the minute and in the future you will be looking at more heat sources and buffer ideal for that.