Advice on work required on boiler

[rach_32]

Hi,

I am after some advice about my malfunctioning combi boiler. I have had a plumber out and he seems like a great chap, just wanted to see if his advice is good.

Okay i have a Bosch Worchester 240 Combi Boiler. back in October hot water completeley failed, central heating was fine. Plumber came out and changed the diaphragm (taking this direct from work sheet so hope it makes sense) this was the advice given on here so i was quite happy.

Great so hot water was working. Since January hot water has become a bit intermitant, sometimes it is fine and very hot other times it is little more than luck warm. It does appear to work best when central heating is switched off.

Just had the plumber back out (same guy) for a service and to look at the problem. He has advised that the gas pressure is not correct, it starts at 4 mbar and works up to the required 14.7 mbar, (sometimes it doen't work its way up, which is when we get warm water). Plumber said the boiler was igniting every time so he didn't think it was a problem with the gas regulator/valve (sorry can't accuratly recall we he called it). actual wording on work sheet: initial opening of hot water tap shows L/MB burner pressure, after a long pause this then reaches the required 14.7 MB - A new DHM sensor is advised in an attempt to solve this.

He has advised we start with changing the domestic hot water sensor first as it is likely this will solve the problem. He says it is best to start here as if we get to changing the gas regulator/valve it will be very expensive and it is best to see if the sensor will do it.

He is also concerned about the availabilty (especially the circuit board if required) of parts as the boiler is quite old?

Does this sound right? Any advice would be apprecaited before i proceed with the work.


Thanks
Rach.

 

[ChrisR]

Well yes, fair line of thought. If it's OK "sometimes" though there's always room for intermittent faults anywhere.

It's easy to simulate a DHW sensor with a resistor, to make the boiler think the water's too cool, whereupon it should make it hotter. That would prove the pcb and gas valve.
Not that they're expensive, it just saves a trip to the shop!

 

[rach_32]

Thanks for the reply,

Doesn't sound like something i could do myself and since my plumber didn't suggest it i don't know if he would try it.

Do i take it that what he is suggesting is a good idea then?

i'm happy for him to carry out the work as long as it's necessary or a good idea, that's what i want to know really.

Thanks
Rach.

 

[ChrisR]

If he hasn't got a spare sensor(£10 or so), or a resistor(1p or so), he can't try it!
But yes, I think what I said answers your concerns.

If you have a screwdriver and small adjustable spanner, you could change the sensor yourself.