Biasi combi - no hot water

[Shafty-Bobs]

The heating works fine and when the heating is on the hot water is fine too. But when the heating is off there is no hot water. I was told it might be the diaphram part number BI1011103 "Central heating pressure switch membrane" which I replaced but it made no difference.
So, here's what happens:-
When I open the hot tap I can hear a whirling noise (fan?) but the burners do not fire up and when I close the hot tap the green light on the front of the boiler flashes rapidly for about 5 seconds and then slows to normal pulse. Is this an indication of something at fault?
I've taken the front cover off and used a cocktail stick to make the connection in the Microswitch (i.e. the pin does come out when the hot tap opens but maybe not comming out fully?) and this results in the burners firing-up and the water temperature from the hot tap fluctuates from luke warm to cold.
Could there be a problem with the PCB or the temp probe or what else?
I hope somebody can help me
Oh, the boiler is: Biasi Riva Compact M90E 32S, fitted approx 7 years ago

 

[bengasman]

Is there no dhw at all, not hot enough, or hot cold hot?

 

[Shafty-Bobs]

no hot water at all when heating is off, i.e. burners do not light up at all.
However, when I did the cocktail trick then the burners do fire-up but the water is warm/cold/warm/cold...

 

[bengasman]

When ch is on, what is dhw like?

 

[Jordon]

Reading it back I would say the thermister but on second glance it may be the motor on the diverter if the pin contacts the micro and the diverter motor dosent switch easy to check pop the motor off and see it the pin inside pops out!

 

[Shafty-Bobs]

when ch is on then hot water is ok, not blistering hot but bearable

 

[bengasman]

Enough to run a bath?

 

[Shafty-Bobs]

when ch is on then having a shower is fine but with the thermostatic settings on the shower valve usually at the max

 

[bengasman]

Diverter is stuck in the middle letting the heat needed to warm he dhw up "leak" into the ch pipes.
You can prove this by letting the system cool down completely, and then turn the hot tap open; ch pipes under the boiler will get hot.

 

[Shafty-Bobs]

Thanks bengasman i think you are on the ball.
dhw is getting into the ch flow pipe which gets much more warmer than the dhw pipe - the temp gauge on the front goes from 25degC to approx 30degC.
So, i've got 2 problems, probaly related.
Firstly the boiler does not fire up in dhw mode
Secondly, if I do make it fire up using the cocktail stick in the microswitch then dhw is mixing into ch pipe.
In your opinion do you think i need to service the diverter valve, i.e. i can buy a kit for about £50, and do you think that will do the trick or is it someat else?

 

[Agile]

I would say that you probably need to replace the diverter motor and the top gland of the diverter valve which will have leaked into it.

Then there is the problem of the pressure switch not being activated. If it woprks on CH then the plate HE may be blocked.

Tony

 

[Shafty-Bobs]

thanks Agile
Do you mean the diverter valve actuator (p/no BI1101102) which is a black thingy on top of the diverter valve? is there a way to check if this is working or not or shall i just replace it (costs about £25).
And if i get the service kit (£50) for the diverter and replace the top glands and o-rings, and clean the HE with descaler - will that do it?

ps: the diverter service kit includes bottom glands too which are more difficult to replace as the valve needs to be removed from the boiler. will i get away with just doing the top glands or am i better doing a complete overall of the diverter valve.
pps: the red light on the dhw flow switch does come on when hot tap is opened so does that mean the flow switch is ok?

 

[Agile]

You only need to change the top gland which can be bought on its own ( although possibly under another makers name.

But you must clean the pin and lube with silicone grease.

You can wait to see if the motor still works if you dont want to buy a new one yet.

Tony

 

[Shafty-Bobs]

Thanks for the help guys.
I've serviced the diverter valve - replaced top glands which came with the kit - the old one was black as was the water that came out from the pump drain tap. Is that a bad sign? do i need to flush and replace with clean water and inhibitor? boiler has not been serviced since fitted some 6 years ago.
Hot water now works even with the heating off but is not hot enough, i.e. only reaches 60degC on guage and if water flow is reduced. Do I need to service the dhw exchanger and how, i.e. remove and flush or replace with new
By the way when i open the hot tap i can hearing a tini noise from the dhw exchanger does that mean i have some metallic crap in there?