UFH Help

[pwater]

Hi

Hoping to get some advice around my UFH. We inherited this system with the house, and while downstairs seems to work quite well, upstairs never seems quite right…

It’s a water system in screed with a solid wooden floor installed over it across the whole upstairs (same as downstairs), however we see very long heat up times in the rooms, and I only seem to be able to get the floors to 23/24 degrees (and subsequently the room temp to around 21) by having 55/60 degree water on my flow, comes back around 45/50

No matter what temp I put in, I seem to always lose around 10 (which I think is right), if i increase the pump speed to full the temp ticks up a few degrees, but no real increase in the speed it heats up.

Have spent ages playing around, two rooms upstairs have no floor coverings atm to check there was no heating being blocked, no draughts i can feel, relatively modern well insulated house (i have been told) just under 20 years old.

One issue is all the flow meters are dirty so i cant really see what they all read, but water does seem to be flowing ok around them (and have had pump on full to test that theory).

My only thought is that the pipes need to travel around 10m before they hit any rooms, so maybe they loose heat in the hallway, but i cant see much evidence of this with the IR gun!

Any pointers appeciated!

thanks

 

[Madrab]

It's not just about temp it's about having the correct flow rates through the loops to give enough time for that heat to transfer into the screed. If you have a return of 45>50deg then the flow may be to high to allow enough time for the floor to absorb the heat.

If you can't see the flow levels then it may be time to flush the system and then get the flow meters off and clean them up.

 

[pwater]

Thanks. Just to clarify from my side (and i appreciate every setup/room is different), what would you expect a floor temp to get to, to give ~21?

Paul

 

[Madrab]

Thanks. Just to clarify from my side (and i appreciate every setup/room is different), what would you expect a floor temp to get to, to give ~21?

Paul

depends on flow temps and output. If it's a engineered wood then it has a max, usually around 27deg, so that would be the normal defining factor. That temp should be easy to reach but with a traditional screed floor then ideally it is left on all the time to maintain the slab temp and stabilise temp outputs.

 

[pwater]

Thanks, and realistically 45 degree input should get the floors to that temp under 'ideal conditions'?

Paul

 

[Madrab]

Ideally yes, it all comes down to environment, output per m2 etc, all it will need is some fine tuning I would suggest. It certainly isn't just about turning up the flow though.

I do have to ask, whey would you want the room temp higher than 21deg anyway, 21deg is really quite warm.

 

[pwater]

Hi

I dont really, its more they just wont seem to go above it, which makes me think something isnt quite right...

Will have a tinker, many thanks for the advice

Paul

 

[Madrab]

Ah ok, yup, fair enough. AS suggested, first place to go is sort out the flow meters, that's key to regulating flow through the loops and therefore heat dissipation

 

[creamola]

I have had a similar challenge to you, so here are some top tips of things I literally last changed/adjusted in Sept:

1. Boiler is Vaillant Ecotec Combi. Despite what is said here AND all the Vaillant documentation, it just doesn't work when you set target temp for Return (as opposed to flow).

2. If boiler LCD temp display flickers between different temps, it's not showing flow/return temps alternatively, the PCB is on the blink. There is an easy fix - look on Youtube (I got into trouble posting it here..). This is important, because it means that the boiler is mis-interpreting the flow temp, so shuts off and goes anti-cycling before you get sufficient hot flow running through that manifold.

3. I replaced the manifold pump with a DAB EVOSTA 3 60/130

4. I replaced the flow regulators with these: https://www.aliexpress.com/item/1005006200371906.html (you can take them off, unscrew the glass tops and clean them out - but given that they are cheap as chips - not really much point).

5. I replaced thermal actuators that weren't working with these https://www.aliexpress.com/item/1005006259715861.html (make sure you get 230V versions and NC (normally closed) if that's the way yours work). [And before anyone shouts about cheap Chinese stuff, mine were EXACTLY the same as the John Guest actuators I removed - except they didn't say "John Guest" on them obvs..

6. I then got some Terrarium Liquid Crystal temp displays (the sort of things you stick on ill kids foreheads) so that I could visually monitor flow and return temps (IR Thermometers don't work that well on copper or PEX pipe).

I have a mixture of floor surfaces served by the UFH - engineered wood, sitting on aluminium spreaders, Limestone tile on Aluminium spreaders and Limestone on solid screed. I set the CH flow to max 60C at the boiler. This results in an average flow temp at the manifold (I just set the adjustable injection therm to MAX) of around 46C. By the time the water is coming out the other end (back to the UFH) it's less than 40C and all told (I have a normal rad circuit upstairs) boiler return flow is in the low 40's (so I get max condensing to boot).

Surface floor temps on limestone/solid screed max out at 24C and just a tad higher for the other surfaces. Everything is fine and nothing delaminates at that temp etc. One final note: because the entire groundfloor of my house is UFH (4 zones) I run this 24/7 with a Vaillant V-Smart (which actually, is about as smart as a box of frogs - but that's another story) with target temps of 17C from 23:00 - 07:00, 19C from 07:00 - 18:00 and 20C from 18:00 to 23:00. In that way, the entire house fabric and contents kind of retains and releases heat, and I don't get that massive temp cycling with down drafts from cold walls and ceilings etc. I have also experimented over successive winters, and I can't tell the gas usage difference between 24hr heating and just coming on when we need it. The only difference is, it now feels cozy all the time and I am averaging a £36 a week gas bill - which includes standing charges and gas for cooking etc. Based on current usage, todays Octopus bill is estimating a yearly gas bill of around £800 - but I have no idea if that's good or bad.

Sorry it was so long - but hope this helps?

 

[ericmark]

Thank you @creamola your idea with stick on temp strips is great.

 

[pwater]

Hi

Thanks, thats some great feedback! I have come a little further with this, I bought a temp monitor with a clamp for flow/return, and it shows that the manifold temp is around 42 degrees, when the mixer shows 50, so may be previously the water going in wasn't as hot as I thought. Great idea on the stick on thermometers, going to do that now...!

Also have worked out that some loops weren't labelled properly, so when we thought we were heating one room, it was doing the hall...how we didnt notice I have no idea, but that seems to be fixed now by moving some heads around.

As I still cant see the flow properly, I have just recieved replacement actuators (went for the salus self balancing) to see if they help at all, as everything else seems pretty good, I have also been playing with the thermostat settings...if I can get to anywhere near your gas bill I will be delighted, as our last one was £1800 for 3 months

Any other advice appreciated but will see if the new actuators do anything!

Paul

 

[creamola]

So,

Hi

Thanks, thats some great feedback! I have come a little further with this, I bought a temp monitor with a clamp for flow/return, and it shows that the manifold temp is around 42 degrees, when the mixer shows 50, so may be previously the water going in wasn't as hot as I thought. Great idea on the stick on thermometers, going to do that now...!

Also have worked out that some loops weren't labelled properly, so when we thought we were heating one room, it was doing the hall...how we didnt notice I have no idea, but that seems to be fixed now by moving some heads around.

As I still cant see the flow properly, I have just recieved replacement actuators (went for the salus self balancing) to see if they help at all, as everything else seems pretty good, I have also been playing with the thermostat settings...if I can get to anywhere near your gas bill I will be delighted, as our last one was £1800 for 3 months

Any other advice appreciated but will see if the new actuators do anything!

Paul

I just turned the mixer up to max, and control the flow temp at the boiler. In that way, I can dial it down to 60C max, which is how I get the above manifold temps.

In any case, are you sure your mixer is, well, properly mixing?

Just to be on the safe side, I bought a service kit: https://www.johnguest.com/gb/en/pro...il-2014/jg-underfloor-service-kit-jg/control2 after discovering that the innards had broken up when I took it apart. It worked a lot better after that, obviously..

In the unlikely event, that you have a Vaillant boiler, I can also supply my config for that - as it's not quite what you would expect.

 

[pwater]

Just an update, incase anyone is interested!

I have now replaced the thermostatic heads on both manifolds, as it seemed they weren't clipping on properly (some strange click clack connection) so the temps were a bit variable. My manifold flow temp is now ~50 degrees and with the salus aba heads I am seeing better heat distribution, i.e the floors are getting to around 23/24, which is giving me 20/21 degrees and keeping everyone happy.

Its still taking a decent bit of time to get the floors to temp, but I think that may just be the nature of the house, no idea what insulation (if any) is under the floor/loop spacings etc.

My last query, and appreciate this may be different for everyone. The boiler (greenstar 8000 35kw) was on for about 6hrs, in that time it burnt through about 11m3 of gas, which on my tariff is around £13 of gas, before I go off down a rabbit hole, does that sound a bit OTT, or pretty standard. It is cold outside (~1 degree).

Thanks

Paul

 

[Johntheo5]

You used 11*11, 121 kwh over 6 hrs = 121/6, 20.17 kwh/hr = 484 kwh/day which would be enormous but this 6 hrs might include warming up the system (water) contents as well?.

In post #11 you said you paid £1800 for 3 months, say 90 days. If gas cost was ~7.5p/kwh, then you used 24000 kwh or ~ 267 kwh/day, seems very high, but how long is a bit of string, I have averaged 14800 kwh/annum (oil) averaged over the past 3 years in a 50 year old 4 bed semi, heating on 16 hrs/day.

 

[pwater]

Hi

Thanks for the reply, the manifold temps flow/return come up quite quickly, prob within 20 mins or so once it is on, so I dont think a massive amount of that time is spent heating really cold water. Currently my manifolds are at around 23 degrees, having been off for 2 hrs or so.

I currently pay 10.3p/kWh (the first ~500 are 15p), seems I am using quite a bit on average per year (~50000Kwh last 12 months), much of which I think was down to the bronze pump running constantly and my water tank then needed constantly reheated, which I fixed a few weeks ago

I suppose I want to get a feel for, if the boiler using that much over 6hrs is 'normal' or is that it really being pushed/is something else at play. It is condensing a decent amount (flow 65, return is around 42), but just seems like alot of gas to feed the 2 UFH manifolds, and top up the water tank after 2 showers.

Ta

Paul