One underfloor heating zone wont heat up

[JeffR]

This is driving me insane..  I have a wet underfloor heating system, with Honeywell Evohome zoning.

Most zones work fine and I believe all zones are labelled correctly. I have one room where the heating is hardly ever used (think I've had it on twice in 2 years), but wanted it on over Christmas. 

 

Despite the controller working, the room does not show any signs of heating (can’t feel anything underfoot).  This is even after leaving heating on for days.

There are two circuits in this room (dunno why, it’s not the biggest room by far), and both show full flow when on.  Grabbing the pipes, flows and returns are hot in both loops which to me indicates nothing is blocked, so why won't it heat up?

[Temp]

I can only think of two reasons..

 

1) Its got a bad insulation problem (no insulation under the UFH)

2) the water flowing in those loops isn't going to the room you think it is.

 

If you don't mind being cold for awhile I'd try an experiment. Before you go to bed turn down all the stats so all rooms are off. Let house get cold over night. First thing turn up the stat for just that room. Check flow and pipe temperatures on that loop warm up (and that no others do). Wait 1-2 hours. Then see if you can detect any change in floor temperature in that room. If not go looking to see if the floors in any other rooms are showing evidence of warming up. 

 

There are two circuits in this room (dunno why, it’s not the biggest room by far)

 

Thats what makes me think the loops dont go to the rooms you think.

 

 

 

 

 

 

Edited January 1, 2021 by Temp

[JFDIY]

Is it a long way from the manifold? - might explain two loops.

 

I would turn the pump up to highest speed, isolate the other rooms, open the glows to max on those two loops and run it for a couple of hours, keep checking supply and return pipes coming out the floor and see if you can detect any heat in the return pipes.

 

 

 

[JeffR]

Hi Temp,

Thanks for the feedback.  Lack of insulation can't be ignored as the builder who installed was hopeless (and has now gone bust).  That said, I can recall that when it was set up, it did work at least once or twice.

It's freezing here tonight, so before I go down the route of turning everything off, I'm going to turn everything on full blast and not timed.  If the floor then heats up, I'll at least know its not a fault and can then start pinning down which zone is which.

Thanks.

Jeff

[JFDIY]

An off the wall suggestion, could they have got the two loops mixed up, so one loop has both connections to hot and the other has both to cold sides of manifold?

 

If you can see the markings on the pipe you may be able to discount this from the Orientation of the text and metre markings.

 

After that you'd have to disconnect one pair of tubes from the manifold and blow down it to see if water is correctly displaced.  Like I say it's s bit off the wall but could happen

 

 

[Temp]

1 hour ago, JFDIY said:

An off the wall suggestion, could they have got the two loops mixed up, so one loop has both connections to hot and the other has both to cold sides of manifold?

 

If you can see the markings on the pipe you may be able to discount this from the Orientation of the text and metre markings.

 

After that you'd have to disconnect one pair of tubes from the manifold and blow down it to see if water is correctly displaced.  Like I say it's s bit off the wall but could happen

 

 

 

I don't think it can be that as he says the flow indicator suggests there is flow.

 

 

[PeterW]

8 minutes ago, Temp said:

 

I don't think it can be that as he says the flow indicator suggests there is flow.

 

 

 does it move when the pump kicks in ..?? Have you got any of the actuator caps..? Take an actuator off and see if the pin moves properly, and also check the actuator operates. 

[Fly100]

Where in the world are you, I have a thermal Camera which could help the issue. We are currently T4 so movement isnt possible, but going forwards after that.

[JeffR]

Morning All,

Thanks the feedback so far.

JFDIY:  Manifold is in the basement.  Room not heating up is in the room directly above.  I have bigger rooms further away, so don't think it's that.  Pretty sure loops aren't mixed (hot/hot and cold cold) as like Temp says, there is flow and both sets of pipes get hot.

Update:

I set everything to 22.5 degC overnight.  Some circuits (kitchen, dining room) I'm familiar with as they come on everyday.  The others are more often set to off, so I'm less familiar and the zones could be mixed without me realising.  The result:  everything pretty much reached temperature APART from the problem room which got to 18.0 deg C.  This room was previously 14.5 before I started al these tests.

The problem room is directly above the basement room and I checked the basement ceiling to see if that was warm (lack of insulation as Temp suggested), but felt nothing.

I'm pretty sure that this room has worked OK in the past, although I've only had it on once or twice since being installed and it could have been when days were warmer?

Could it be that the loop needs bleeding? But that said, it does show flow and both supply and return pipes are hot..

 

[PeterW]

I’d go for it being a duff actuator not opening fully then. Very low flow would do this. 

[JeffR]

59 minutes ago, PeterW said:

I’d go for it being a duff actuator not opening fully then. Very low flow would do this. 

Testing again this morning with actuators removed (meaning valves open).  Let's see!

[Temp]

3 hours ago, JeffR said:

JFDIY:  Manifold is in the basement.  Room not heating up is in the room directly above.

 

Air lock? 

 

If that turns out to be the cause make sure there is corrossion inhibitor in the system after its been sorted.

 

Edited January 2, 2021 by Temp

[JFDIY]

3 hours ago, JeffR said:

Manifold is in the basement.  Room not heating up is in the room directly above

 

Are these the only loops that are above the manifold? What position are they on the manifold- close to the pump side? (Photo may help)

 

 

My money is on them being full of air, you are seeing some flow along the base of the pipe, but a fair proportion of the pipe will be air.

 

If you think of it, for every air bubble that enters that loop will rise into the room and without sufficient flow (difficult to achieve in normal use) there is little chance of driving them downhill on the return side.

 

You can try turning off all other loops, then setting the pump to maximum and turning on the problem room, isolate each of the two loops one at a time and run for an hour or so.

 

You may wish to remove the actuator and manually pulse the flow control PIN in and out to dislodge the air.

 

If the manifold has an auto bleeder, make sure it is open, otherwise keep trying the manual bleed screws to keep air out of manifolds.

 

If the above doesn't work, you may need to isolate the manifolds from the CH circuit and pressurise the hot manifold with a hosepipe, then try bleeding each loop as above.

 

 

I guess this has been a gradual change, or as there any work carried out that would have allowed air into the system?

 

I guess any time you do any work you need to isolate the manifold, or preferably wind down the flow meters and ensure the actuators are removed to isolate those circuits from any air ingress.

Only once the system is then re-bled of air would you re-open them. 

 

 

[ProDave]

4 hours ago, JeffR said:

JFDIY:  Manifold is in the basement.  Room not heating up is in the room directly above.

 

Yes, new information.  Those loops will have filled with air.  It is very bad practice to feed a room above the manifold as even if it works to start with, it will collect every air bubble in the system.

 

A manual hose pipe purge will get it working but you really want to insert an air bleed point in the loop at it's highest point which might not be a trivial task.

 

Can you post a picture of your manifold?

[dpmiller]

I've an upstairs loop in ours, and tee'd an auto vent into both flow and return where it rises up and heads into the FF screed. Works perfectly, just need to remember that it'll drain down if the system is depressurised elsewhere.

[JeffR]

Hi All,

I so appreciate everyone's input on this.  I'm no plumbing expert, but like to at least understand the problem before handing it over to a grown up....

 

To address PeterW's comment re actuator:  I removed both actuators today and let run for 7 hours.  Only reached 18.5 deg C.  Can just about feel some warmth underfoot, but pretty dismal.

Hallway next to this room is sitting toasty at 21C.

So, I'm really hoping its an air issue.  If indeed it is, would the flow levels still indicate full flow?

 

I'll try and take more photos tomorrow, but my system comprises:

• Boiler at the top of the house. There's a manifold next to boiler.  Will investigate what's attached to it tomorrow.  
• All upstairs rooms on radiators, except for 1st floor bathroom which is wet underfloor. (All work fine)
• At ground level, i have kitchen, hallway and living room (which is the one playing up).  All underfloor.
• There's a family room on a level halfway between ground and basement. (its a weird split level house).
• In the basement (where main manifold is), there's a bedroom, a bathroom and an office.

I take on board the comments about manifold should be below loops, but I have at least three other loops above the manifold that seem to be operating fine.  I'm really hoping its just just this one that's got air.  It's only been on 2 or 3 times in 2 years.

 

JFDIY: Before I look into a hose pipe bleed, how do i manually set pump to maximum??

 

Thanks everyone..

 

[Temp]

I think its possible to have full flow even with air in the pipe. The air bubble acts like a narrowing of the pipe so water moves faster while going past it.

[Temp]

15 minutes ago, JeffR said:

Before I look into a hose pipe bleed, how do i manually set pump to maximum??

 

Sometimes there is a rotary lever/knob on the pump. This one is set to max = III

 

 

[AdamSee]

I would go with a airlock aswell. I have ufh pipes above the mainfold and also had to install air bleeding vents at points higher than the floor.

Could you close all of the flow regulators except for the room that's a problem and listen out for air movement comming thought? That would give a reasonable indications as to how much air is in the pipe. 

After starting my system up after the summer months it took about 2 days to stop gurgling from settled air in the pipework.

 

 

[JeffR]

'Temp', I just had a look at the pump (Grundfos UPM3 Auto) and downloaded the manual.  I'm not going there regarding manual control!!  It's some kind of load controlled device and the settings are already different to the factory pre sets, so I think its safer to stay away from that.

 

Here's a few shots of the system:

Pic 1:  Manifold next to boiler.  Boiler is in loft.  One loop (without actuator) just goes from supply to return, so I guess this is doing nothing.

The other loop I think, is the upstairs bathroom.

Pic 2:  On both supply and return manifolds, there is this 'pot'.  Has a Schrader valve on top and what looks to be a hose coupling underneath.

Pic 3: The manifold in the basement (below the room that won't heat). 

 

How do I go about bleeding or am I in expert territory now??? (I am a mechanical engineer, reasonably confident, but not reckless!!)

 

AdamSee: I don't hear any gurglings..

[PeterW]

Those pots are auto bleed valves. Push the pin down and any air should escape. 

[dpmiller]

What's the red hose with the T-pieces?

[JeffR]

40 minutes ago, PeterW said:

Those pots are auto bleed valves. Push the pin down and any air should escape. 

Aha..  I'll try that.  Will have to be tomorrows job now.

 

20 minutes ago, dpmiller said:

What's the red hose with the T-pieces?

Part of the fire sprinkler system and totally separate from everything else..

[paud100]

Hi JeffR

 

Did you ever manage to fix this issue as I have the exact same issue in my house and it’s driving me insane as well?! 
 

Any help would be appreciated. Thanks. 

[Temp]

1 hour ago, paud100 said:

Hi JeffR

 

Did you ever manage to fix this issue as I have the exact same issue in my house and it’s driving me insane as well?! 
 

Any help would be appreciated. Thanks. 

 

Welcome to the forum.

 

A few people have had air trapped in a loop. If that's the problem connecting hoses to force water through the problem loop at speed appears to be the recommended solution. Once that's done you need to ensure there is enough corrosion inhibitor in the system as the gas is a corrosion product and it can/will come back.

 

Check other things first like flow meters. If water is flowing through the loop then air is about the only easy to deal with problem.