Biasi M90E 28S No H.W unless C.H is on

[davros1979]

Hi guys,

I an new to boilers so go easy on me.

I keep intermitently getting no hot water and have worked out that when the C.H is on it always works. When the problem occurs the boiler doesnt even fire, I then switch the heating on and it fires straight away and I can get H.W.

Done a little research, think the service manual is pointing me at diverter valve, HW flow switch or regulation ignition PCB.

Are there any tests I can do to see where the problem lies?

 

[Agile]

I expect the DHW flow switch is not reliably operating.

The earlier ones used a clip on Hall effect detector just to the left of the pump which illuminates a red LED when it senses DHW flow.

If that is not always sensing the flow then it needs a reg gas engineer as the gas valve needs to be removed to access the shuttle which will be sticking.

It also seems the diverter valve is also not operating totally correctly.

But like many things, without being in front of the boiler its not always possible to diagnose the exact problem without a succession of tests.

Tony Glazier