Biasi Riva Compact - no hot water unless heating has fired

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12 Mar 2014
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Staffordshire
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United Kingdom
Hi

I have a Biasi Riva Compact m90e 28s.

On many occasions, when the hot water is called for it runs
cold and the boiler doesn't fire up.

If the heating is on hot water runs fine. Also if the
heating is activated and turned off even after a
second then hot water will also work ok.


The green indicator on the control panel also
flashes rapidly with no lock out indicator (when
the water is not working).

Would it be diverter valve or flow switch for DHW??

Any ideas?

Cheers

Peter
 
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If I remember rightly, those boilers have a magnetic flow detector on top of the diverter valve.

It's a little white cap and has an little green light on it. When there is flow though it it has a small led. I'm sure I've had this issue with this exact boiler in the past. It can be a bit of debris stuck in the valve.

I'm not saying this is the only issue but just drawing on a past experience.
 
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The M90 does not use the part that you have linked to.

The DHW demand switch might not be working but even if that were the case then the diverter should not allow any hot water to be produced.

So my best guess is that the DHW demand switch is not working and the diverter valve is leaking.

There are different later models but the earlier demand switches needed the gas valve to be removed to work on them so cannot be a DIY repair.

So it needs to be properly diagnosed to establish the exact problem. That will probably need an experienced engineer!

Tony
 

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