Biasi M90.24s coming on when not programmed

[livefast]

Hi people

I have a biasi M90.24s boiler that has worked fine for about 5 years, Just recently i noticed it keeps firing just for 10 seconds or so when its not programmed to come on. The problem seems to be getting worse and the wife says she had to get out of bed at 2am to turn the heating off last night. The programmer says the heating is off but the rads are hot and the boiler is fired. The domestic hot water is working fine and the heating is coming on when programmed to do so. i've turned the stat right up to 30 degrees but still its coming on when not required or programmed.

anybody got any ideas.

cheers mark

 

[Agile]

This would usually be as a result of an unwanted frost protection operation.

It may just be dirty contacts on the sensors. Slowly remove and replace the plugs a few times and see if this improves the situation.

If not then let boiler become cold by removing mains supply for an hour and measure resistance of each sensor with plug removed. Should be about 13 K.

Tony

 

[MUFC1999]

If pulling the plug off and putting them back on doesnt work for you, there is a micro switch, bottom left hand side as you look at boiler, has a clear housing a common fault on these is the spindle leaks, causing moisture inside the housing which intermittenly makes the switch without anything being on, as the diverters on these rest in the CH pos when the boiler fire due to the moisture it heats the rads, let us know how you get on.

 

[Agile]

1999, you are refering to the older 24S.

This is an M90 model with a motor operated diverter valve!

 

[MUFC1999]

1999, you are refering to the older 24S.

This is an M90 model with a motor operated diverter valve!

I am talking about m90e.24s G.C. 47 970 17 it has a motor operated diverter and it has the microswirch in the clear housing on the front, where the moisture gATHERS am i on the right boiler, if its that G.C. no then what i said stands

 

[Agile]

In that case then the switch you are referring to is the system flow switch.

It is not the DHW demand switch!

Operating it when there is no demand for heat will not have any effect.

Tony

 

[MUFC1999]

In that case then the switch you are referring to is the system flow switch.

It is not the DHW demand switch!

Operating it when there is no demand for heat will not have any effect.

Tony

Ha ha what a **** i look sorry, its just a pump proving switch isnt it