Vokera Excell Flow Rate Dropping?

23 Feb 2006
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United Kingdom
I have an Excell 80SP Combi, which recently had a problem with the water temperature varying.

Temp would sometimes run hot & drop to tepid, but not every time (only when 'our lass' was wanting a bath - LOL). Eventually, happened for me! Flow rate from tap was set same as normal so cause was not too much flow.

Also, when running tap & water was hot, flow rate would fall. Had to keep opening tap slightly to maintain same flow.

Changed both domestic & flow diaphragms yesterday. Flow diaphragm looked as good as new but domestic had started to break down.

Water temp appears to be hot & stable again (60 ~ 65 degrees). Time will tell (probably when she runs the bath tomorrow morning). However, flow rate still dropping when water heats up from tap.

Also, when working on boiler noticed gentle 'rattling' noise from somewhere in the hydraulic assembly. I think the noise has been there for a while but since I've noticed it, it's getting on my wick! Sounds a bit like unbalanced fan, but it's not the fan. Rattling stops when CH switches off.

System pressures seem stable at 1 ~ 1.5 bar.

Does anyone have any suggestions on what the cause of the noise may be & why the water flow rate drops when the water heats up?

Could the two be connected?
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Its quite a common problem on modern taps that the flow rate will slow down. You should set the flow at the boiler and this might solve your temp problem
Thanks for the reply. I will try that. The water temp has been fine since I changed the diaphragms.

Any idea on the noise on the boiler? It sounds as if it may be coming from the domestic heat exchanger? Sounds like a wind-up clockwork toy!

As I said, now I have noticed the noise, it's really annoying me.
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probably scaled up

this will explain the drop in water flow and the noise

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