Old boiler has pump overrun issue

[dmart7]

I have an old Apollo 60B which is running well but has an intermittent boiling issue. It seems to be connected to the pump overrun stat but it works correctly most of thetime and I would be grateful for advice. Intermittently – once every few days - water boils in theboiler for a few seconds (banging and swooshing). This only occurs on the “LO” boiler stat andwith central heating running.It does notoccur on “HI” boiler stat nor if heating water only.The boiling and banging occurs only immediatelyas the boiler relights after cycling off via the “LO” thermostat, and only if,by chance, the pump overrun stat has just switched off the pump.

Normally,once the boiler has been on for more than half-an-hour (say), on “LO”, itbegins to settle down to a cyclic process:

1. Theboiler heats for 10-15 mins, then the LO stat trips off the gas
2. Thepump runs on for a minute or two (overrun stat), then it goes off
3. After3-10 seconds, the pump turns on again
4. Afteranother minute or less, the boiler relights

If the boiling and banging occurs, it comes after about 80 minutes from cold start and happens when the boiler relights (4) a split second after the pump goes off (2) above. It seems that on one chancecycle, the overrun stat switches off the pump just as the boiler relights and the pump doesn’t restart (3).As the pump isn’t on, the water boils immediately, it bangs loudly for a few seconds and the burners are switched off by the thermostat.

Iam inclined to think the overrun stat is faulty but am not sure exactly howthey work and whether the way this one switches off and on, or notoccasionally, is at fault.

 

[Last Plumber]

You need a gas safe registered engineer to look at that for you. The Over run stat is inside the boiler and you should be registered to work on a gas appliance.

The only advice I would give regarding your boiler is that it is very old and is probably due for replacing. I've not worked on those for a long time. It must be 30 years old nearly now.

It's done well !

 

[Last Plumber]

You need a gas safe registered engineer to look at that for you. The Over run stat is inside the boiler and you should be registered to work on a gas appliance.

The only advice I would give regarding your boiler is that it is very old and is probably due for replacing. I've not worked on those for a long time. It must be 30 years old nearly now.

It's done well !

 

[dmart7]

You need a gas safe registered engineer to look at that for you. The Over run stat is inside the boiler and you should be registered to work on a gas appliance.

The only advice I would give regarding your boiler is that it is very old and is probably due for replacing. I've not worked on those for a long time. It must be 30 years old nearly now.

It's done well !

It has done well (25 years) but I don't want to replace it any earlier than I need to. Its not the money but the switch to a condenser boiler and some of its physical requirements (subject for another day). The boiler has been seen more than once by gas engineers. Because the fault can't be reproduced during their visit, they have taken the simple view that it is old and scaled. Which I accepted until I studied what was actually happening - using patience and video equipment. I am hoping that someone who reads my description can help diagnose before I invite them again.

 

[jtsplumbing]

Main problem you will get is availability of spare parts, not come across one of these for a long time Is it the Thorne or Myson Apollo ??

 

[dmart7]

Main problem you will get is availability of spare parts, not come across one of these for a long time Is it the Thorne or Myson Apollo ??

It is Myson. I can see the parts on various websites, including the pump overrun stat. It seems likely that the behaviour reflects a fault in the overrun stat....?

 

[Dotty]

And you've been told you need a gsr. Stop fishing.

Thread closed.