Glow worm back boiler

[Paulo11]

Hi

I have a Glow-worm back boiler which is giving me grief (I would have upgraded it by now but its a listed building and there's issues with venting through the external wall and I'm reluctant to go with an electric boiler instead (because of the consumption cost)). It's a sealed system. The problem is that overheat stat keeps activating.

Sometimes it lasts a week without a problem and sometimes (like this morning) it lasts about 30 seconds before tripping.

The heating engineer has been out a number of times and, amongst other matters, Changed the overheat stat, Changed the thermocouple, Changed the gas valve, Bled the radiators and Checked the pump, TRV, pressure vessel, pressure gauge, cylinder etc.

There is a small leak somewhere in the pipework (as the pressure gauge, which is set at over 1 bar, drops by apx 0.5bar every 24 hours); the plumber is coming to look at this although not sure if this will deal with the boiler problem.

Seems very odd that it's so intermittent (e.g. how can an overheat stat work fine for an entire day and then activate 30 seconds after firing on the next day).

Not sure if air in the system would cause the stat to activate (irrespective of the boiler temperature) although no sign of air in rads.

I'm at my wits end with this so any input would be greatly appreciated.

Thanks

Paul

 

[ShaunCorbs]

Does the system have a pump overrun ? Also the baxi back boiler wasn’t designed to be sealed so I’m surprised it’s not leaking

 

[Paulo11]

Does the system have a pump overrun ? Also the baxi back boiler wasn’t designed to be sealed so I’m surprised it’s not leaking

Thanks for the reply Shaun

Not sure if there's a pump overrun but I've attached a photo of the pump.

No signs of any leak in the boiler itself. Its a Glow-worm 56/2 BBU unit. I've got the manual (attached) which says this model is OK in a sealed system.

Difficult to know what to do next (especially as the boiler itself hasn't been used much over the years and is in good condition).

I get the feeling that the source of the problem isn't the boiler itself (pump, pipes?) but banging my head against a (cold) brick wall at the minute.

ATB

Paul

 

[ShaunCorbs]

I would try running the pump on a plug and see how you go eg before you want heating plug the pump in then wait a min then turn the heating on

It says it’s only suitable for sealed if at time of ordering it is said etc was yours always sealed or been converted eg no header tank ever?

 

[Paulo11]

I would try running the pump on a plug and see how you go eg before you want heating plug the pump in then wait a min then turn the heating on

It says it’s only suitable for sealed if at time of ordering it is said etc was yours always sealed or been converted eg no header tank ever?

 

[Paulo11]

Thanks; I'll give that a go with the pump.

I suppose a malfunctioning pump would quickly set off the overheat stat if the hot water isn't being pumped away from the boiler. Might also explain why the fault is intermittent (if the pump is flaky).

Either that or there isn't enough water in the boiler in the first place (although the system pressure seems OK at 1bar+).

I cant think of anything else that would set off the overheat stat.

It was a sealed system from Day 1.

ATB

 

[Freexicor]

I once had a similar experience with my old boiler acting up, and it turned out to be the result of a tiny leak in the system causing pressure fluctuations. It sounds like you're already on the right track with having the plumber check for leaks. Sometimes, those little things can cause big problems! Hang in there, and hopefully, you'll get it sorted soon.