Central heating Pump Overrun

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This will work, but you might have to add a second relay to the pump, as you'll be feeding volts to it which may then go somewhere else that they shouldn't, as it were, with the system 'off'. That's what happened with mine. I never bothered working out exactly why, but IIRC it caused the system to fire continuously.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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In an earlier contribution to this discussion,

I can't see why you'd need a second relay. I drew a circuit diagram before posting the above, and satisfied myself that, with the single relay as described, the boiler firing will cause the pump to run but *not* vice-versa.
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wrote:

Thank you for your reply Set Square. Your solution looks very elegant to me and I see no reason why it should not work. I propose to implement it as soon as I can.
Malcolm
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In an earlier contribution to this discussion,

Please let us know how you get on!
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It's just been pointed out to me that it will be necessary, of course, also to install a by-pass for the valve which controls the central heating water flow, otherwise the water will have nowhere to go!!
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In an earlier contribution to this discussion,

That depends on the system design. If it's an S-plan where all the zone valves will be closed, then yes you need a by-pass. If it's a Y-plan with a mid-position valve, there is always a path open somewhere - unless *all* the radiators have TRVs (at least one of which shouldn't have!) and they are all closed.
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I added this feature to mine. ISTR I had to change the pump switching to a mains relay, as simply feeding mains to the pump after the thermostats were satisfied caused problems by feeding those volts elsewhere - although that might well not be the case with others. I made the timer circuit which is set for 30 seconds. Basically, a small low voltage power supply, a 555 timer and a relay. Cost nothing as I had all the bits lying around, but probably no more than a tenner to buy.
At the time, I investigated finding a ready made unit but couldn't. And, of course, most boilers have these built in now.
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On Sun, 4 Jan 2004 10:52:36 -0000, "Malcolm H"

Yes it did. I used to have one until a year and a bit ago.
The pump over-run is provisioned by a separate set of contacts on the thermostat. Either the pump was never wired to them, or as on mine, the thermostat has failed.
When I enquired regarding the cost of a new one it was in the 70 range. Since this followed a failed thermocouple (that admittedly only cost 2 to replace) I decided that the boiler was at the end of its useful life. These things are a piece of junk anyway. I was never able to dismantle it without cutting myself on sharp metal somewhere.
Considering also that they run at 65% efficiency at best, I felt that spending money on a new thermostat was pointless and put it towards the cost of a new condensing boiler instead.

You could do this with a stairway lighting timer.
Have a look at rswww.com part number 277-3520
It has a mode whereby the output remains on for a time after the input drops.

.andy
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Having spent most of today poring over Glowworm manuals, I can say with a fair degree of certainty that it doesn't

Yes there are several, but if this has started happening recently, it would make sense to find out why it's happening rather than bodging it
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Mine definitely did, although thinking again it was installed in 1985.
From the Sedbuk web site, there was a Fuelsaver 40-50b (identity 4131583) which was last manufactured in 1983.
There was a Fuelsaver 50Mk2 (4131320) which IIRC is what I had. It was range rated from 11 to 14kW and I'm pretty sure said something like 40-50 on the outside case.
Perhaps the over-run was the Mk2 feature....
Either way it's time it was in the skip.

.andy
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