Boiler overheat thermostat keeps tripping

[dazzystar]

Hi All,

We had a gas engineer come to fit two new zone valves. It took him ages to try and get the air out of the system. The issue now is the boiler stat trips every few minutes so something isn't right.

It's a Potterton Prima 60F.

Could it be air still trapped as I heard one of the rads gurgling earlier?

Cheers
Daz

 

[Dan Robinson]

Yes. Sounds like and air lock.

 

[dazzystar]

Cheers Dan. Any recommendations on clearing the air out. I've tried opening the rad bleed valves but all I get is water!

Not sure if this is relevant but I've shut off most of the rads thermostatic valves as we don't want to heat those rooms but if you think I should open them all up then let me know.

Cheers
Daz

 

[Agile]

Turn on the heating and close one valve on each rad except one! Usually just close the TRV.

Then open the next and close the first and so move the open one round the house until all have been run open for about three minutes each.

Then usually that will have cleared it.

Tony

 

[dazzystar]

Cheers Tony.

Just tried opening up the two rads which I closed and pressed the trip on the boiler. It fired up for a minute or so and I heard loud knocking sounds from the boiler and it tripped again. I've turned it off for now.

Just so I understand you correctly are you saying to close all the rads in the house except one and then open up another valve and close the one I opened a few minutes before and repeat?

Cheers
Daz

 

[dazzystar]

Tony,

Re-reading your post again, do you mean leave the bleed valve open on one rad and not shutting off the TRV?

Cheers
Daz

 

[Agile]

You had obviously closed ALL the rads so there was no flow!

You must always keep ONE rad open so the flow can go that way!

Tony

 

[dazzystar]

You had obviously closed ALL the rads so there was no flow!

You must always keep ONE rad open so the flow can go that way!

Tony

3 rads downstairs were on but I opened up the 2 rads upstairs and fired the boiler up and that's when I heard the loud knocking from the boiler and it tripped.

 

[dazzystar]

Had the central heating on last night for 2 hours before I heard the boiler knocking and it cut out. One thing I noticed this morning when I left for work is that the overflow pipe sticking out from my loft had obviously been dripping as the roof slates were wet.

I have the electric immersion on all the time at the moment as we must have hot water in the morning (and boy is it hot). Not sure if that's relevant or not.

The only other thing I can report is that 2 rads in the house I couldn't bleed yesterday despite opening the bleed valves. No water came out so they may be blocked I guess.

Any thoughts?

 

[garethpa]

You say you have turned off most of the radiators as you don't want to heat those rooms. By doing this, the water won't have lost much of its heat by the time it gets back to the boiler, potentially causing your boiler to overheat cut-out. Normally, if this happens, it should really pause, then resume when things have cooled down a bit.

What is the heating temp set to on your boiler? If it's at max, then this may be why it is locking out requiring a reset. Perhaps turn the temp control for the heating down on your boiler.

It's a good idea to actually use the TRV's to control temp - perhaps keep them set at 1 instead of off. This provides a gentle bypass, plus prevents them getting stuck closed.

You should actually have one radiator without a TRV valve. This should be left on at all times as itself provides a bypass in the event that all the TRV's are closed.

Not getting any water out of the two radiators suggests they are isolated from the central heating. Are these two radiators fed by the same zone valve? If so, it may be in the closed position. Were the new valves verified working?

 

[dazzystar]

You say you have turned off most of the radiators as you don't want to heat those rooms. By doing this, the water won't have lost much of its heat by the time it gets back to the boiler, potentially causing your boiler to overheat cut-out. Normally, if this happens, it should really pause, then resume when things have cooled down a bit.

What is the heating temp set to on your boiler? If it's at max, then this may be why it is locking out requiring a reset. Perhaps turn the temp control for the heating down on your boiler.

It's a good idea to actually use the TRV's to control temp - perhaps keep them set at 1 instead of off. This provides a gentle bypass, plus prevents them getting stuck closed.

You should actually have one radiator without a TRV valve. This should be left on at all times as itself provides a bypass in the event that all the TRV's are closed.

Not getting any water out of the two radiators suggests they are isolated from the central heating. Are these two radiators fed by the same zone valve? If so, it may be in the closed position. Were the new valves verified working?

Thanks for the reply.

I opened all the TRV's in case this was causing the issue. The rads which I can't bleed do come on though. The boiler was set to its lowest temp setting. Could it be that I had the immersion on and the hot water somehow is ending back up in the F & E tank in the loft?

 

[Madrab]

You should actually have one radiator without a TRV valve. This should be left on at all times as itself provides a bypass in the event that all the TRV's are closed.

Unless your system has an auto-bypass fitted?

 

[dazzystar]

You should actually have one radiator without a TRV valve. This should be left on at all times as itself provides a bypass in the event that all the TRV's are closed.

Unless your system has an auto-bypass fitted?

Rad in the bathroom doesn't have a TRV fitted (mind you I installed the TRV's on most of the rads a few years back).

 

[twgas]

Why were te zone valves replaced?
Coupled with the fact you've had them done, can't bleed rads and overflow issues I'd bet you've got a fair amount of sludge and blocked/restricted pipework. Try running a magnet round the pipes at the point where the cold feed and open vent join the system.

 

[FiremanT]

Errr.. What does the plumber who fitted the valves say?