Boiler pump runs continuously

I have a Baxi Genesis combi boiler.
Yesterday, I noticed that the pump was running all the time.
I played around with the settings and found that Hot water is fine, but no CH. My wife did briefly turn on the CH yesterday and it did come on.
If I select CH, the boiler will fire up but go off within 20 seconds or so. The pump continues to run.
I assume it is a sticky / duff microswitch in the 3 way valve and I need to get it replaced. Does that sound right?
As it is the weekend, and I would prefer to wait until Monday (plumbers are cheaper then), will it cause any problems or damage if the pump continues to run?
Obviously I don't need CH at this time of the year, so am just happy that we have hot water.
Steve......
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Presumably the pressure is OK? What does the pressure guage show on the boiler?
Toby...
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Yes, pressure is normal.
Not lost any or gained any.
Steve....
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I am slightly confused here, you say it is a combi boiler, so the hot water is heated as it is needed, you dont have a hot water cylinder, right?
If so, why is there a three way valve in there for?
What pressure is the guage showing on the boiler?
Toby...
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Yes, a combi boiler. No tank. (Baxi Genesis 80)
It does have a 3 way valve. Manuf'rs Part number 235838.
Pressure is 2.
Steve.........
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At the moment I have powered down the boiler and am only powering up when we want hot water. I am concerned that damage will be done if the pump is running 24/7 even when there is no demand for CH, and CH is turned off anyway.
Should I be concerned about damage being caused by the pump running 24/7?
Steve.......
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dog-man wrote:

Not if water is circulating..but if you have a duff microswitch, and the water valve is closed, the pump will be circulating against a blockage, and unless there is a bypass, it will be working hard to no avail.
The fact that the boiler short cycles indicates there is no circulation, so your guess at a stuck or welded microswitch seems reasonable.

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The boiler manual states that it has an integral pre-set bypass and that all radiators can have a trv because of that.
Is that the bypass that you mention and is it therefore safe to leave the pump running until I get it repaired after the weekend?
Steve.....
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From my limited experience the pump is powered from the boiler and is required to continue pumping after the boiler goes out, to ensure there are no hotspots in the heat exchangers. One result is that you generally require a bypass valve to ensure that water can circulate through the boiler.
I suspect that no damage would occur to the pump. If anything I would check that the pump body doesn't get too hot!
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Its not a good idea to make assumptions regarding boilers if you don't actually know - there are too many variables
I can't see the OP since he's a googlegroupie, but I think it is prolly the diverter valve switch
so does ...
http://www.google.co.uk/search?hl=en&q xi+genesis+manual&start&sa=N
which took 10 seconds to google
--
geoff

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Thi is my original post...

Yesterday, I noticed that the pump was running all the time.
I played around with the settings and found that Hot water is fine, but no CH. My wife did briefly turn on the CH yesterday and it did come on.
If I select CH, the boiler will fire up but go off within 20 seconds or so. The pump continues to run.
I assume it is a sticky / duff microswitch in the 3 way valve and I need to get it replaced. Does that sound right?
As it is the weekend, and I would prefer to wait until Monday (plumbers are cheaper then), will it cause any problems or damage if the pump continues to run?
Obviously I don't need CH at this time of the year, so am just happy that we have hot water.
Steve......
<<<<<<<<<<<<<<<<<<<
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dog-man wrote:

probably yes.
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Now fixed.
It was the 3 way valve.
Steve......
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