Glow Worm Micron 60FF Overheating

[PGMonkey]

Hi folks

The boiler is a Glow worm Micron 60FF and is about 8 years old, it recently had a service with thermistor replacement.

Since then, the boiler has twice stopped working (after successfully heating radiators) and displayed the green reset light. The first time it happened was a few weeks after the service, the second time was this week.

It's hardly any trouble as I just need to turn the boiler control to 0 and then back to the previous setting. The pump continues to run, the only sign of a failure is the lack of radiator heat.

The manual says a solid reset light is due to overheating but I'm curious as this has never happened before. Could it be related to the new thermistor or might it be something else? I did some research and have found comments about faulty PCBs and thermistors on this model and other Glow Worm models.

I've turned the temperature dial on the boiler down, to about 3/4 and all appears to be fine, for now...

FYI, the pump and Y-valve in the airing cupboard are about a year old. The boiler flue fan was replaced a few months ago.

Thanks

 

[PGMonkey]

Just a quick update - since turning the level on the boiler down a little, it hasn't overheated again.

I understand the thermistor's resistance changes according to its temperature and the PCB uses that to regulate gas flow.

So, do you folks think it's likely to be the newly installed thermistor that is faulty?

 

[PGMonkey]

Does anyone have any ideas about this one?

 

[MeldrewsMate]

I understand the thermistor's resistance changes according to its temperature and the PCB uses that to regulate gas flow.

Not so, the gas flow is regulated by a combination of the gas regulator in the gas valve, and the injector size.

The thermistor could be at fault, allowing the boiler temperature to become higher than the overheat thermostat will allow. The o/h stat is independant of the PCB and will need to be manually reset, so you'd know if it'd operated.
In that way turning down the desired temperature will disguise the problem.

Max. temp should be 82C, and that is very hot for a radiator surface temperature. Can you confirm that by holding your hand on the rad for 5 minutes? If the skin blisters immediately, or is left behind on the rad then it's probably over 80C.


Alternatively you could use a thermometer!!!
Most people get by with a 70C flow temperature or lower.