Strange Boiler Issue (Glowworm)

[Boiler_Boiler123]

I've got a Glowworm Flexicom 12hx Condensing Boiler.

We inherited it with the house and the previous owners didn't keep up with servicing etc. so it's never been top draw but has kept us going for a couple of years now.

The problem at the minute is that when heating water (heating is off at this time of year) the boiler is showing the lit 'flame' icon as normal, increasing the temp from mid 70 degrees up to 85 at which point the lit flame icon disappears and the temp reduces back down to mid 70s again. This then repeats for the duration of the water heating period. The water's heating fine and there's no error codes.

Is there anything I can do to prevent this from getting worse - which I suspect it will!

Thank you!

 

[Johntheo5]

I think the Glowworm is a close relative to the Vaillants, on some of these the max temp setting via the control knob is 75C, (see below from a Vaillant ecotec plus 418).

 

[Boiler_Boiler123]

Would that mean it's overheating and switching it's self off to cool. Then repeats?

 

[Harry Bloomfield]

Would that mean it's overheating and switching it's self off to cool. Then repeats?

Could it mean that it is not getting rid of the heat it is generating, into the HW cylinder, fast enough? Is there a range rating setting, so you could reduce the Kw output, when HW is being called for?

 

[Johntheo5]

The problem at the minute is that when heating water (heating is off at this time of year) the boiler is showing the lit 'flame' icon as normal, increasing the temp from mid 70 degrees up to 85 at which point the lit flame icon disappears and the temp reduces back down to mid 70s again. This then repeats for the duration of the water heating period. The water's heating fine and there's no error codes.

If you can increase it to 85C then the flow temperature should increase over a few minutes to 85C, if the heating coil then can't absorb enough heat the flow temp will increase to 90C (or close to it) the burner should then trip and will refire when the anticycle time has elapsed and the flow temp is < 80C.
What is the cylinder stat setting?.

 

[Boiler_Boiler123]

If you can increase it to 85C then the flow temperature should increase over a few minutes to 85C, if the heating coil then can't absorb enough heat the flow temp will increase to 90C (or close to it) the burner should then trip and will refire when the anticycle time has elapsed and the flow temp is < 80C.
What is the cylinder stat setting?.

The cylinder stat is set to just over 60c

 

[Johntheo5]

Actually increasing the flow temp should result in more heat being absorbed by the heating coil so less of a problem.
Is the boiler behaving like I asked in post #5??.

 

[Boiler_Boiler123]

Actually increasing the flow temp should result in more heat being absorbed by the heating coil so less of a problem.
Is the boiler behaving like I asked in post #5??.

Yeah, pretty spot on what you said

 

[Johntheo5]

Theres not a lot you can do about that but I'm a bit surprised that a flow temperature of 85C (with a cylinder stat setting of 60C) is causing the boiler to recycle since your boiler should modulate down to around 4.0kw or so?. Check and see if there is a balancing valve installed on the cylinder coil return, and if a gate valve with a wheel, ensure its at least one full turn open. I have no balancing valve on my cylinder coil return and a 70C (average oil fired boiler) flow temp results in the coil absorbing ~ 8.0kw when the cylinder temp is cold at 25C but it only absorbs 2.5kw when pretty hot at 55C.