Boiler fires up when heating and hot water are set to off.

colourblind

Had our Glow Worm Micron 40FF boiler and Megaflo system for a few years now, already fitted to the house when bought it, and it has always randomly switched itself on for only a few minutes even with the timer settings, Danfoss FP715, set to off.
It's something I've got used to over the years but, I will soon be renting out the house and I think it should be looked at.

A friend of mine, not local, who is gas safe but not unvented qualified, thinks it's really odd and thought it might have been the Danfoss unit. He said to switch off the boiler and remove the unit from the back plate and switch it back on. After about 20 minutes the boiler started up again, so presumably the controller is not at fault. He also thinks it could be the way the Megaflow system is wired up as he believes they can be configured different ways.

Has anybody experienced a similar thing?
Is this normal for a megaflo system?

Obviously. I will need a unvented qualified plumber to take a look/work on the system but it would be useful if anyone has an idea of what the problem could be and I wont be ripped off.

southcoastrgi

when the boiler fires up do you know if either of the two valves have opened up ie either the one going to the heating or the one going to the cylinder, what i mean is are you sure it's the cylinder or that valve that is causing the problem, does the pump switch on when the boiler fires ?

sancho

I had the same problem with my back boiler system, it turned out my actuator switch was sticking on. Replaced it and all has been good since.

Not sure if your system even has one, but worth looking into. It looked like this.

zzzLazyDaisy

Sorry if this is a stupid question, but have you checked the handbook? My boiler fires up every 90 mins or so, when the heating and hot water are off. If is designed to do this (I forget the reason, possibly something about keeping the pump working?). Anyway, there are separate indicators on the boiler for when it fires up for water, heating, and this 90 min routine fire-up.

colourblind

southcoastrgi wrote: »

when the boiler fires up do you know if either of the two valves have opened up ie either the one going to the heating or the one going to the cylinder, what i mean is are you sure it's the cylinder or that valve that is causing the problem, does the pump switch on when the boiler fires ?

Hi southcoastrgi

When it fires up the pump runs, and the hot water valve opens but can't work out whats calling it.

colourblind

zzzLazyDaisy wrote: »

Sorry if this is a stupid question, but have you checked the handbook? My boiler fires up every 90 mins or so, when the heating and hot water are off. If is designed to do this (I forget the reason, possibly something about keeping the pump working?). Anyway, there are separate indicators on the boiler for when it fires up for water, heating, and this 90 min routine fire-up.

Hi zzzLD

have checked the handbook for both the boiler and the megaflo system but there is no mention of it!

gas4you

I would hazard a guess that the hot water zone valve is stuck open, rather than opening from an 'unknown' demand, thereby constantly keeping the boiler etc on.

Turn off all power to the heating system and see if you can hear of feel the valve shut.

If it doesn't you need a complete new valve fitted.

Also, if this is the case, you now don't have the zone valve working as a 'safety device' for the unvented cylinder.

colourblind

gas4you wrote: »

I would hazard a guess that the hot water zone valve is stuck open, rather than opening from an 'unknown' demand, thereby constantly keeping the boiler etc on.

Turn off all power to the heating system and see if you can hear of feel the valve shut.

If it doesn't you need a complete new valve fitted.

Also, if this is the case, you now don't have the zone valve working as a 'safety device' for the unvented cylinder.

Hi gas4you, thanks for your reply

Would this then allow the boiler to turn on for about 5 minutes and shut down, then repeat this process every 1/2 hour or so?

The hot water port is defo receiving voltage to open the valve when it fires up, can see the lever moving and hear the motor turning, but from where the supply is coming, I really don't know!!

Myser

A stuck microswitch in a zone valve can cause a boiler to fire continuously however, a zone valve actuator can only open if the programmer is enabled for heating or hot water and the respective thermostat is calling for heating/hot water.

With the programmer removed and a zone valve actuator still opening, there is clearly something wrong with the wiring.

colourblind

Myser wrote: »

A stuck microswitch in a zone valve can cause a boiler to fire continuously however, a zone valve actuator can only open if the programmer is enabled for heating or hot water and the respective thermostat is calling for heating/hot water.

With the programmer removed and a zone valve actuator still opening, there is clearly something wrong with the wiring.

Thanks Myser, I think you are right, there must be a fault within the wiring somewhere.
Would you recommend an unvented plumber or an electrician to investigate?

Jonesya

Has your system got a thermostat and/or pipe-thermostat to protect the boiler against frost - say if it's located in the attic/garage/out-house?

These are wired by-pass the controller to switch on the boiler and pump regardless of the what the controller is doing, to protect against frost.

A fault on one of these could call in the heating, it might be something minor like them being set too high so calling on the boiler when not required.