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.

 

[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.

 

[Ermintrude]

each manifold has its own pump at the manifold not in the plant room. Manifold picture earlier in the thread.

Hi, sorry on an iPhone.

Ok so you have zv on each manifold.
Don't like the 4 port blending valves. Difficult to balance. I prefer pump/ manifold return and primary flow. And then a balance-able return. Notice there is no pipe stat to tell the zv when flow is needed. So it's just open when manifold is on? Not much point in it. IMO , should have a pipe stat set on the returns from floor to blending valve and be set so that when flow cools and blending valve opens up for more primary heat and interlocks with boiler or in your case the LLH pump.

Also what is floor construction? Just that there is no conduit on the ufh pipes as they leave the floor? Always try and have 150mm of conduit above floor and 350 is below to protect from mechanical damage.

 

[JusKel]

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

If that is the main pump, then why is there a tee between it and the boiler?
Can you remove it and connect in to left side of pump ?
Or maybe move the pump onto the pipe coming directly off the boiler?
(Mentioned previous too)

 

[Jedny]

Any chance of bigger pic

 

[Ermintrude]

Any news?

 

[diamondgas]

Hi Carrera, To get the IR working you can paint the pipe black 🙂

Scenarios with testing .... I'd want to know what strain was being put on the boiler, so primary F&R's would be where I'd monitor under as many load scenario's as possible up to max load. If your flow temp drops below 60 DegC it'll start to draw heat out of the cylinders hot water. If the flow temp stays cool for a long time then I'd be pointing towards that being the reason why your hot water isn't getting to temp!

If you haven't already, I'd put the hot water on 24/7 or at least an all day setting.... 🙂

 

[Carrera]

Sorry haven't been able to test much at all, as the system is not really working as it was left for the holidays. At the moment just about able to get warm water, boiler going on and off very 2 mins and the heating was working with a light load, but has now started doing the same. Will have to wait for the plumber to come back next week before I can really try anything

 

[diamondgas]

Give Worcester a call, your boiler is under warranty with them. You may have a fault on the boiler?

 

[Carrera]

Give Worcester a call, your boiler is under warranty with them. You may have a fault on the boiler?

For the hot water, basically boiler fires, flow temp rises (set to 70), modulates lower and lower and kicks off when it goes over 70, water circulates for a couple of mins and then when temp hits about 40 boiler fires again, slowly getting to 70, before we go back round the loop. As you can imagine water takes ages to warm up this way, so have been combining thus with the emmersion over the holidays. I will give wb a call on Monday.

does not do this on heat, gets to 70 and stays there, however this morning started doing above with heating, but after a few attempts of me stopping and starting the heat, it appears to be ok.

 

[diamondgas]

For the hot water, basically boiler fires, flow temp rises (set to 70), modulates lower and lower and kicks off when it goes over 70, water circulates for a couple of mins and then when temp hits about 40 boiler fires again, slowly getting to 70, before we go back round the loop. As you can imagine water takes ages to warm up this way, so have been combining thus with the emmersion over the holidays. I will give wb a call on Monday.

does not do this on heat, gets to 70 and stays there, however this morning started doing above with heating, but after a few attempts of me stopping and starting the heat, it appears to be ok.

Without seeing what's going on it's difficult to give you anything accurate to be honest Carrera! Are you able to get a reading on the return as the flow is heating? If so there should be around 20DegC difference, thereabouts. If there's a rapid rise in temp to 70 before dropping back to 40 then I'd be wanting to know how well the pump was performing and/or is there a potential flow restriction somewhere? If the rise is gradual and there's a maintained 11-22DegC difference between F&R then Circulation is okay IMHO 🙂

 

[Howsie]

This one really needs eyes on IMHO.

 

[Gray0689]

This one really needs eyes on IMHO.

I agree something just ain't right even apart from the under sizing IMO

 

[diamondgas]

:iagree: without 1st hand knowledge there's strange goings on being described...! It'd be handy to have to op's plumber on here to give us the heads up on what they've done so far! Doubt they'd like some of the chatter in the thread mind! 🙂

 

[albatross]

Carrera, I have a good read of this and it's the kind of problem that needs a site visit. It's a shame you are so far from me, I'm in Yorkshire, as I would have liked to have got my teeth into it and solved it for you. Saying that try this:

Turn hot water on, turn one underfloor manifold on upstairs, close all the lever valves at the top left of the photo, see if the cylinder heats, if so you have a severe balancing problem.

This may make no difference but it's worth trying. Modern cylinders have high resistance coils and the circuit to the manifolds will have a low resistance as the underfloor pumps take over the work after that.

 

[huddster]

Would it not be worth putting some gate valves on before the lever valves to restrict the ufh circ and towel rads to test weather it is drawing the heat away from the hot water, just a cheap option that might get you by until you figure out a more permanent solution

 

[Ermintrude]

Could just close ball valves ?