Fagor FEB-27E combi boiler problem

[Penfold69]

Hi, when i turn the hot on water i can hear a micro switch clicking, but the boiler doesn't fire up. If i leave the water on it will fire up after a little while, then it will cut out and in again constantly, giving cold water then really hot,then cold to hot, can anyone help please
Paul

 

[MANDATE]

From my understanding of a combi, when the hot tap is opened it releases the pressure on one side of a small diaphragm which makes the diverter valve move to cut off the circulation through the radiators and divert the hot system water to a heat exchanger. So cold water enters the heat exchanger and comes out hot.
If the boiler does not light I would think either the diverter has not moved far enough to trigger the micro switch or the micro switch contacts are dirty/burnt and not making a good contact.

If the boiler does light, The problem could be that heat can not transfer from system water to cold water passing through heat exchanger. This would allow the system water to get too hot and the boiler stat would switch the boiler off.
After a cooling off period the whole process could repeat itself.
Split or holed diaphragm affects the movement of diverter valve.
micro switch contacts dirty/burnt gives intermittent or no contact.
scale in heat exchanger acts as insulator and reduces the heat transfer.

 

[Penfold69]

Hi, thanks for your quick reply,a for the diverter valve i only had a new one fitted at the beginning of the year, so i'm going to check out the micro switch I'll be back in touch with the results

 

[TCCHeating]

Post deleted: thinking of the wrong boiler!

 

[Penfold69]

Hi i took the micro switch off, ran the water and activated the switch several times. Everything seems fine now, it's been running ok for the last two days.So if it does it again I'll replace the the switch.Many thanks for your help.