Biasi Prisma 24s Provides Heat nut no DHW

[lixxie]

Hi

I have a Biasi Prisma Boiler, apporximately 7 years old. It has many faults over the years and the latest has me completely stumped. Having only just replaced the fan less than 12 months ago, I now have an issue wherein we have no hot water.

When I turn on a hot tap upstairs, even at a trickle, the boiler fires up and the water eventually runs hot. Then, inexplicably, the boiler emits a banging from somewhere around the top region of the case (near the fan) and then the boiler switches off (the pin pops out at the bottom). Strangely, at a relatively slow run, I can get a sink full of hot water in the kitchen (the room next to the boiler).

I have replaced the hot water diaphragm to no effect.

Can anybody identify what the problem is?

 

[bellairaphon]

i don't know this boiler but whats the flame picture like when this banging occurs

Nath

 

[lixxie]

Hi

Actually, the flames reduce in size when there is a demand for hot water. Incidentally, when the hot water tap is runnig the temp guage shoots up from 60 degrees to in excess of 130.

Thank you for replying.

 

[bellairaphon]

whats the central heating doing same?

 

[lixxie]

NO. The boiler behaves differently. Flames are larger and temp. is a constant 60.

 

[bellairaphon]

does it have a seperate domestic hotwater heatexchanger? does it have a divertor valve. like i said i dont know the boiler

 

[lixxie]

Got a sink of boiling water in the kitchen now with no issues. Yet, when tried to run a bath upstairs the noise re-occurred and the boiler switched itself off (pin popped out).

 

[bellairaphon]

id be looking at a blocked dhw heat exchanger

nath

 

[lixxie]

Iam not sure about the valve. I assume that it does have one. It's a wall-mounted combi. I know there is a split valve with a diaphragm for hot water and a diaphragm for the heating.

Sorry I am not being much use.

 

[bellairaphon]

im gunna have to leave this one to someone who knows the boiler n layout. but with wat u have said id be looking at the dhw heat exchanger n divertor. sorry im not much use to u

Nath

 

[lixxie]

It's fine. I really appreciate your help so far.

Cheers.

 

[1oldspindle]

Hi lixxie, sounds like you need a diaphragm replaced. A kit for that boiler would cost about £40.oo. but get a RGI to do it and have it serviced at the same time.
Hope this helps.

 

[Agile]

It is probably just a blocked plate HE.

Change/clean that and it will probably be all thats needed.

Tony