Biasi Boiler No DHW

[cy.dewhurst1]

I have a Biasi Riva boiler. In CH mode, it ignites fine, runs fine, seems to regulate when you turn the CH temp down etc. - as soon as you open a tap and the DHW kicks in, the temperature guage shoots up from about 55 to 90, then it shuts down (without locking out). I have to reset to get the CH back. Effectively, whenever you turn the tap on - you get 10 seconds of increasingly hot water, then the boiler gets switched off by the safety thermostat.

Any ideas?

I've put more water in the system, as it was down to below 0,3. It's now up around 2,0 - which is probably too high (believe it should be

1,0), but didn't seem to make much difference. I thought it might be something to do with the pressure?? ie. not pushing enough water through, so it was heating too quickly and triggering the cutout, but apparently not.

I've taken the housing off of the circuit board, and checked all the connections - nothing seems a miss, but I'm kind of thinking it's maybe the logic - or the DHW potentiometer on the board or something.

I'm presuming it's not the temperature sensor, as the CH works and regulates - and it's clearly nothing to do with the gas - or the supply. Could the DHW element be blocked or something?

[Ed Sirett]

Yes.

It wouldn't see Sealed CH FAQ.

I thought it might be

There maybe more than one temperature sensor, indeed it is quite common for there to be separate sensors for CH and DHW. Given the sudden onset of the problems this is a probable cause.

Yes that would also give these symptoms.

[agileservices]

Perhaps you have called a professional to sort this out by now?

At first sight it might appear to be the temperature sensors. ( Green things ) They should measure about 11 K at room temperature, less if the boiler is warm!

However if the temperature goes so high then I would expect the plate heat exchanger is blocked and needs to be cleaned or replaced.

I dont understand how you say it shuts down, without locking out, but then say you have to reset it ! There are two resets the overheat stat and the flame failure which gives the red light.

Tony

[Doctor Drivel]

What for? This is a DIY group.