Underfloor heating - one room cold

[TD]

New-build flat, Geminox THI-5-25-M75 combi boiler with inbuilt tank, and underfloor heating. I think something is wrong, as per old thread

I have been able to fill the bath successfully on full power, by making sure the temperature is set to no more than about 36degC. Still not truly satisfactory, as it should be able to chuck out a bathful of water at a much hotter temperature, at full power. We're waiting for the engineers to come and take a look, it's taking a while as they're not getting on too well with the builders. Anyway...

When we first moved in, the underfloor heating was crap. One of the builders' workmen came in (jack of all trades), and opened a panel which provides access to valves for the various underfloor heating circuits. Each circuit has a flow-rate gauge, and they were mostly down at zero.

He did *something*, the gauges went up, and the heating was suddenly better. But now, I think it's becoming worse again. I'm pretty sure that one room in particular isn't heating up in a meaningful way. Looking at the panel, 11 out of 12 circuits show around 1 l/min, and the other shows nearer to 2. There's a temperature gauge fitted in the send pipe, and it currently shows about

33degC. According to the boiler control panel, water pressure is 2 bar.

Can anyone help? Do the above vital stastitics look normal? How can I go about narrowing the issue down?

[Richard Russell]

Are all your underfloor loops connected to a common manifold? If so, the only reasons for one running at a lower flow rate than the rest are the setting of the valve for that loop (if there is one), the loop itself being much longer, or some kind of blockage. Be aware that the flow gauges sometimes stick (two of ours read maximum even when the system is off!) so check that before taking too much notice.

That's on the low side for UFH, I would say. Ours (Polypipe) is set to 40C and I think it's safe to run it a little higher than that. Check with the manfacturer's data though, because you don't want to risk underfloor damage by setting it too high.

Richard.

reply by email change 'news' to my forename.

[TD]

They are indeed all connected to one manifold. What's weird is that when I checked just now, one of the flow gauges had gone down to 0, so I had one on

2, one on 0, and the other ten on 1.

I'd say that no loop should be *that* much longer than any other, obviously there are differences, but it's a bog-standard 1400sqft flat with a squarish shape, so nothing is *that* far away.

Hmm. I wonder if that is related to the problem with the bath not being as hot as it should. I wonder if there could be more than one problem. *sigh*

Also, why do some circuits have those "things" on top, and some don't, and could they contribute to the problem? The one on 0 doesn't have one, the one on 2 does.

There's a photo of the manifold at

- a picture tells a thousand words etc.

[Tim Lamb]

Is each loop controlled by a local motorised valve and does each room have a thermostat?

My room stats, supplied by Polypipe, are battery operated and I suppose you could have a working display but insufficient power to operate the relay.

If you have individual room controls, you could shut off several loops by lowering the thermostat settings and then see what flow rates you get and where. Poor pump performance could be an issue but outside my experience. (all my pumps have failed noisily rather than lack of output).

Ah! Photo!

I am not a plumber.

You appear to have a 12? way manifold with all pipe loops connected. The system looks to be coupled as two groups, presumably with the control valves electrically linked together.

The loops with the blue covers should not be functioning.

Maybe the installers decided 6 loops were sufficient for your needs?

Others will know more but I have found the Polypipe site explains the intended operation of their system clearly.

regards

>

[Richard Russell]

From your photo, and as Tim pointed out, it looks as though six of your loops have individual 'motorised' valves and the remainder are manually balanced, which is not a configuration I've encountered (your motorised values are in the open position). Mine has motorised valves on every loop (note that the valves are very slow acting because they operate by thermal expansion of a wax).

Not shown in your picture is the thermostatic diverter (assuming you have one!) which reduces the flow temperature in the hot-water circuit

- which is probably in the range 60-80C - to the temperature required by the UFH - about 40C. Let's hope your system isn't trying to run both the UFH and the hot-water cylinder at the same flow temperature - that would never work satisfactorily (but might explain your problems)!

Here are a couple of pictures of my system:

first thing I'd do is to get your flow temperatures right; for the HW circuit I use 65C and for the UFH 40C. The HW temp is probably set on your boiler, and the UFH temp with thermostatic diverter (mine is very similar to a TRV, as you can see in the picture, but there are other types).

Richard.

reply by email change 'news' to my forename.

[Richard Russell]

Reading your old thread, I see that you have a combi boiler so you can ignore my comments about the HW cylinder. If the *only* thing being fed from the CH output from your boiler is the UFH then you may not need the thermostatic diverter, in which case the flow temperature will most probably be set at the boiler, but I don't know whether a standard combi will work satisfactorily at such a low value.

Richard.

[TD]

Well, there is a main thermostat in the hall. (It was originally installed in the sun-facing lounge until we asked them to move it. *sigh*)

There are "slave" thermostats in both bedrooms, but my understanding from the boiler manual is that these can be used only to /lower/ the temperature in that room. So what do I do? Turn the one in the cold bedroom down, and see what happens to the flow-rate gauges?

Yes, three of the valves have 1 written on, and the other three have 2 written on. What do these valves actually /do/?

Hmm, they are all showing flow rate of 1L/min except the one that has mysteriously gone to 0, and the one on 2. Which is now nearer 1 again.

I wonder if the two groups are related to the two slave thermostats, and the other circuits (with the blue caps) are somehow controlled by the main thermostat.

I don't know, I'm really confused now. To make things worse, AIUI the boiler and heating were installed by different contractors. I think I just need to get them down here and find out what they were trying to achieve and why it's not working properly.

According to the valves, mine is Polyplumb. I have downloaded

and will give it a look through.

[The Natural Philosopher]

I've got a self installed system virtually the same.

The way I set mine up is this.

1/. in this weather, I run the temp reducing valve as hot as the thing will go. 50C and a bit going INTO the floors.

2/. I have a master thermostat on a zone that has NO separate valves on it.

3/. You balance a system like this by removing ALL those blue caps and all those thermo control valves and adjusting the zone screws - square shafts- that are exposed and checking the loop flow gauges. All other things being broadly equal, you want the same flow through all zones. that way the same watts per meter of pipe will be put into the floor.

4/. The clip on control valves with the wires coming out are just hot wax capsule heated by small heating coils, that press down on the balancing spindles, push them in, and halt the flow. These will work very much like TRV's.

5/. If you screw the alternative blue caps down hard, this has the same effect. It shuts down the zone. I use this to control zones in parts of the house we don't normally heat except for guests.

What you need to do is identify which zones feed your problem room, and check they have flow. They may have no flow because you screwed the blue caps down hard, or because the wax capsule things think the room is warm enough, if its statted. Or because they are ill balanced.

If they have full flow and the room is still cold, your only recourse is to up the temperature going into the whole UFH unit. That's a big blue knob to the right of the manifold on my polyplumb installation, anyway.

[TD]

I don't understand why it would be like this. As I said in my reply to Tim, I think I need to get the installers in and find out what they were thinking. I'm assuming you're saying the valves are open because the blue bits at the top are visible?

As per your follow up, it's a combi. I've checked the boiler statistics on the main thermostat and they say: Outside actual: 5degC Oustide min: 3degC Outside max: 7degC Room actual: 22degC Room min: 20.5degC Room max: 22.5degC DHW actual: 64degC Boiler actual: 41degC Flow actual: --- Burner modulation: 0% Water pressure: 2.0bar

The pilot light symbol seems to be on most of the time.

If I assume (which is never great!) that "Boiler actual" is the heating circuit temperature, then why does the UCH manifold show 33 on its thermometer? With that evidence, and the previous thread about struggling to quickly fill a bath above 38deg, I'm really starting to wonder if this boiler has a problem.

[Tim Lamb]

Mine seems OK.

The on/off temperature swing is quite large 10 or 12 deg. but the thermal mass of circulating water quickly brings this below 50degC. once the boiler stops firing.

AFAICT the boiler operates in the eco mode according to the display and the amount of condensate it produces.

Have I misunderstood the operation of the control valves? I assumed they would be normally closed: energise to run.

regards

regards

[Tim Lamb]

In message , TD writes

No.

If there is a *master* thermostat in the hall I guess the circulating pump will not run and the boiler not fire up for heating unless the hall temperature is below that set.

Try setting the hall stat to a higher temperature and see what happens.

These are electrically operated controls for the valves which are fitted in the cold side of the manifold.

From what has been said elsewhere, I may have misinterpreted the operation. It rather depends if the valve hidden under the blue cover is open or closed. If the normal condition is *open* then your system appears to have *background* heat from the uncontrolled circuits (regulated by the hall thermostat) and local control from the slave thermostats.

You will have to turn up the hall temperature.

Those flow indicators are a bit uncertain. There should be a square key to operate the adjusters but the system ought to have been balanced by the installers so... on your own head!

regards

>

[TD]

Aha, so that's why some of mine don't have valves.

Ah. Interesting. Mine currently look pretty similar, mostly 1L/min. Circuit

12 (on the far right) is a little higher, around 1.5L/min - surely that's not enough to matter much?

Got it.

That explains why one was showing 1 and then later 0 after I took the cap off to have a look and screwed it back on. Fixed it now. :) I don't think it's the problem though - the cold room has been bad for days or weeks, and I accidentally switched that circuit off yesterday.

It looks like all zones have flow.

I think my combi should be responsible for that. It just doesn't seem to get hot enough.

[The Natural Philosopher]

Nope. Normally open, energise to shut off...I think..

Could be wrong..

[Richard Russell]

That fits with there being motorised valves only on some loops (those that feed the bedrooms). Presumably your main thermostat controls the boiler and those UFH loops which have no motorised valves, and the bedroom thermostats allow those specific loops to be shut down.

You need to identify whether the problem is inadequate *flow rate* or inadequate *water temperature*, or both. You said previously that the flow temperature was 33C; that's far too low. The Polyplumb guide to which you linked quotes a range of 45-55C for solid (screeded) floors and 50-60C for suspended/floating floors. So sort that out first.

Once you've got the water temperature right, and assuming the bedroom is still too cold, you will need to investigate the flow rate. If both the bedroom thermostat and the main thermostat are calling for heat the motorised valves for that bedroom should all be open (blue ring visible) and the gauges should show maximum flow. If any of the loops for that bedroom are showing a reduced rate, you could try unclipping its valve; that should give you a clue as to whether the valve isn't opening fully or there's some blockage/constriction elsewhere.

I presume the three marked '1' control the heating to Bedroom 1 and the three marked '2' control the heating to Bedroom 2. The function of these motorised valves is to shut off the UFH in those bedrooms if the roomstats aren't calling for heat.

The caps will have been fitted either simply to protect the valves, or to allow manual balancing of those loops. If your only problem is the bedroom temperature(s), I suggest you leave them alone.

One of the first things I did after moving in was to label all the UFH circuits so I know exactly which ones feed which rooms (see my first photo). This makes diagnosing a problem much easier.

Richard.

reply by email change 'news' to my forename.

[The Natural Philosopher]

One thing to note, is if you have pipe in concrete, the thermal time constant is DAYS not minutes, or hours.

You should run that 24x7 in this weather.

My UFH auxiliary pump is 3 speed. middle is best.

You want a good 10C drop between the inlet and outlet manifold if you are running low temps.

even a blasted combi (spawn of devil) should be able to get outflow up to 50C+ which is all the UFH can handle anyway.

I would also note that in general, from cold, the UFH runs the boiler flat out for about 4-6 hours here, before the room temp starts to climb appreciably. And the cats migrate from the aga to the corridor where all the pipes run..;-) best thermal sensors I have really.