Baxi 105he - no hot water at low flow - diaphragm?

8 May 2007
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United Kingdom

got a problem with my Baxi 105he. I've installed some new taps in our house - kitchen a couple of years ago, and bathroom washbasin at the weekend just gone. Problem I'm having is that when running the kitchen hot tap it doesn't fire up the boiler, or has to be stopped and restarted a couple of times before this happens.

With the new ikea washbasin tap in the bathroom it's not firing up the boiler at all. But when we turn the bath hot tap on the boiler starts up fine, and keeps running as long as we need.

I suspect this is a problem with the diaphragm. I've done work on this bit of the boiler before - changing (I think) the gland nut a couple of years ago when there was some water leaking through it.

Anybody able to confirm if this sounds like the diaphragm? I do also have a periodic problem with pressure drop in the system which I think might be due to a leaking bleed valve on a downstairs radiator - is this likely to be connected to the symptoms we're experiencing with the boiler?


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It does sound like diaphragm fault, and a loss of system pressure can be caused by a water leak. Diaphragm kits are about a tenner, and an easy diy job.
ok - thanks for the reply. I've picked up one of these kits before - got some plumbers merchants near my work so easy enough.

I'll give it a go this weekend.

If its not the diaphragm then its the venturi fell apart just above cold inlet , getting quite common fault
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if necessary, is the replacement of the venturi something I can do - or is it one for a Gas Safe engineer?

Better to measure the flow rate at which it just switches on.

That should be about 2.5 litres per minute!


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