UFH system stopped working properly!

[Radboy]

My wet UHF system has recently stopped working properly. the boiler is a Worcester 30CDi which connects to the UFH system via a Horstmann motorised valve. the manifold has a mixing thermostatic valve and a Grundos UPS 25-60 pump. everything has been working perfectly for about 12 months until 2 weeks ago when I put the Salus 500RTF wireless thermostat onto the frost setting when we went away for 4 days. When resetting the thermostat to come back on everything seems to work for about 5 minutes and then the Horstmann valve closes and the pump goes off. I've checked everything i can think of but cant work out why the valve closes and the pump switches off.

• Thermostat calls for heat, green light comes on on receiver box.
  Orange light come on on Horstmann Actuator Valve
  Valve opens (clicking sound can be heard and no resistance on manual override lever)
  Pipe between actuator valve and UFH manifold gets hot
  Flow Pipe below manifold and Pump to UFH gets hot
  Pump come on
  Sounds like water is moving on both Flow and Return pipes
  Howvere after a few minutes the valve closes and the pump is switched off.

The green light on the thermostat receiver is still on however although the Thermostat is calling for heat the valve is closed and the pump is switched off.
The return pipe doesn't get hot and seems to get very slightly warmer but because it switches itself off after only a few minutes any temperature change is negligible.
Everything on the flow side is very hot but the return side is cold.
The CH to the rest of the house is controlled by another motorised valve and works perfectly.
The UFH system is heating a concrete slab approx 6 by 5 meters.
Please help, all family members and friends have been exhausted! Any ideas welcome?

 

[SimonH2]

Is there any secondary/safety stat on the UFH ? I believe some systems have a stat to shut the UFH down in case it gets too hot - to avoid damage to pipes/floors.

 

[Jordon]

Have you turned the boiler stat up to a higher level of heat? As above most ufh systems will shut down if the flow is two hot, maybe the bypass valve isn't working correctly since you shut it down so the flow no longer mixes correctly via the bypass. What ufh do you have? Also salus wireless are carp switch the reciver to manual

 

[Radboy]

Thanks for the comments

Yes there is a stat on the UFH manifold to control the temp of the flow going into the system, I've set this on max.

I think you are on the right lines, the stat maybe switching the system down because it is getting to hot. i'll try turning the temp down on the boiler so that it doesn't get so hot and see if this works.

The Salus receiver doesn't have a manual switch, just an on or off switch, so i cant switch it to manual.

Not sure what type of UFH it is. It wasn't an off the shelf piece of kit. the manifold is a H shape with a speedfit mixing stat in the middle, below this is the grundos pump which is connected to the pipework.

Thanks for trying to help, it'd really appreciated, I'll try lowering the boiler stat and see if this stops the valve closing.

 

[SimonH2]

That would account for it shutting down.
It's possible the TMV is stuck or faulty, thus making the flow temperature too high. Turning the boiler temp down will mask that, but the root cause will need fixing.

 

[DeltaT2]

You need to start where you stopped, link out the Salus stat first, try that.
Then double check the UFH circulation pump is working, then ensure there's no air in the UFH loops.............Sounds to me like an air lock?? But I don't know as I'd need to see the installation.

 

[Radboy]

Turning the boiler stat down to 3 didn't fix the problem I'm afraid, presumably it's not the manifold stat that faulty.

Sorry I dont know how to link out the Salus stat, there isnt a manual on or off switch to the UFH? It seems to be working ok though, when I increase the temp on the stat it calls for heat, the receiver light comes on and the valve opens. 5 minutes later the Horstmann actuator valve is shut closed. When this happens the Salus receiver light is still on and the themostat is still calling for heat. Do you think it is an electrical problem with the Salus controls, it seems to be fairly constent problem though, i.e everything works as it should then after 5 minutes it closes the valve and shuts down?

My thoughts were also an airlock but how can one get in? The system has been working for over 12 months without any problem. It is a new installation of plastic pipes encased in a concrete slab. If it is an air lock how do I get it out? Isn't the pump strong enough to push it round untill it gets to the CH system where I will be able to bled it?

Thanks for your help

 

[SimonH2]

Sorry I dont know how to link out the Salus stat

You'll need to power down the whole system and remove the fuse so it can't be turned back on while you are working on it.

Then remove the stat receiver and put a temporary wire link across it's output terminals (or move both wires to one terminal). This means the stat is doing nothing and the system will see a call for heat all the time.

The reason for doing this is to positively rule out any problem with that particular bit of equipment.

It's called "diagnostics". At present you have many things that could be responsible for the problem. You need to eliminate as much as you can until you pin down the problem. This particular action is cheap (no cost) to do and will allow you to rule out/in the Salus stat as a candidate.

If, having disabled it, the problem persists - then you can rule it out and look for another candidate. If the problem has gone - then you can rule it in. The alternative (and one that seems popular with many people) is to keep fitting more and more new parts (at the customer's expense) until the problem goes away or you run out of parts to change.

Of course, I'd have some test gear out and be looking at the electrical system - looking to see which switch/stat/programmer/whatever is turning off the supply to the zone valve. But if you don't have any test gear or don't know how to use it safely then it's not a good idea to do this - don't forget you'll be working with mains voltages, possibly while holding/leaning on a nice conductive earthed pipe

 

[DeltaT2]

Turning the boiler stat down to 3 didn't fix the problem I'm afraid, presumably it's not the manifold stat that faulty.

Sorry I dont know how to link out the Salus stat, there isnt a manual on or off switch to the UFH? It seems to be working ok though, when I increase the temp on the stat it calls for heat, the receiver light comes on and the valve opens. 5 minutes later the Horstmann actuator valve is shut closed. When this happens the Salus receiver light is still on and the themostat is still calling for heat. Do you think it is an electrical problem with the Salus controls, it seems to be fairly constent problem though, i.e everything works as it should then after 5 minutes it closes the valve and shuts down?

My thoughts were also an airlock but how can one get in? The system has been working for over 12 months without any problem. It is a new installation of plastic pipes encased in a concrete slab. If it is an air lock how do I get it out? Isn't the pump strong enough to push it round untill it gets to the CH system where I will be able to bled it?

Thanks for your help

In a year old system, there's a bigger chance of an air lock. Most UFH manifolds have auto air valve, cause it can be a 'high point' in the system.
HTH

 

[SimonH2]

If it were an airlock then I can't see why the system would be shutting down. With no flow round the system, there's be no hot entering, and nothing to trigger any over-temp limit stat.

If there were flow, due perhaps to the main system pump pushing it through, then I'd expect at some point for the UFH pump to spring into life - if there's water going round, then it's going through the UFH pump. Given any flow at all, an airlock would (I'd have thought) get churned into small bubbles and eventually expelled through the UFH system and out to the main system - probably to settle out in the rads elsewhere.

Another question to the OP - is it always "5 minutes" ? Or does it vary - eg could be 2 mins, could be 10 mins, but generally something "around 5 mins" ?

 

[Radboy]

Thanks SimonH2
There is flow through the UFH manifold and it does kick the pump into life. I'll time it tonight and see how long it takes before the valve is closed to see if it is an exact time or if not what the range of times are.

 

[DeltaT2]

Thanks SimonH2
There is flow through the UFH manifold and it does kick the pump into life. I'll time it tonight and see how long it takes before the valve is closed to see if it is an exact time or if not what the range of times are.

This may prove my point, who knows?? Is there any actuator heads on the manifold loops mate??

 

[Radboy]

Typical, I cant now get the actuator valve to open. Before, when I raised the temperature on the wireless thermostat so that it calls for heat, the actuator valve would open, the flow would start, the pump would fire and then after a few minutes the valve would close and the pump would switch off. Now the valve won't open at all. I have a green light on the receiver and an orange light on the valve but nothing is happening. There is a manual override switch on the valve which I have opened and locked into the open position, I expected this to start the flow and fire the pump. The flow did start but the pump didnt fire. I left this in the open position for 10 minutes but the pump didnt start. Could this be because it is fired by an electrical signal in a sequence, i.e. open valve then fire pump or do they normally work on pressure or flow? It seems to me that either the valve or the controller is faulty. The pump is a Grundos ups 25-60 it has two plastic boxes to the side of it, one is obviously the speed control box, which is set on 3 and the other is a grey box which has a wire coming from the controller and one going into the pump, I presume this is just a connection box. Do you think the problem is electrical and that the valve prematurely shutting/now not opening is due to a faulty controller?

There are two actuator valves which control whether the flow goes to either the UFH or CH system, the CH system has its own thermostat and controller and is working fine. The actuator valve for the UFH isn't on the manifold itself but on a branch of the pipework that leaves the boiler.

Thanks for your continued help and advice.

 

[Agile]

moving a valve manually does NOT produce the electric signal used to control the next action ( depending on how its been wired ).

Tony