Central heating Pump Overrun

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I have a Glow-worm Fuelsaver 40-50 conventional flue boiler which was installed in 1984.
Everything works fine except that the central heating circulating pump stops running as soon as the room thermostat reaches the desired temperature. This results in some noisy bubbling from the boiler as it overheats for a short time after the room thermostat switches the pump and boiler off.
Does anybody know if this boiler was designed to have a pump overrun feature to avoid this problem?
If the boiler was not designed to have a pump overrun feature is there a control available which can be added retrospectively. e.g. is there a timed control available which will allow the pump to run for a short time after each switch off?
TIA
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Malcolm H wrote:

How bizarre: I've been wondering about exactly the same problem, with my Glow-worm Hide Away. It's slightly younger than yours, possibly 1986 or so.
I think it's quite wasteful to have all that recently-heated water suddenly come to a halt, rather than circulate it for a short time to spread it around. Also, as you mention, it causes kettling which must in turn reduce the life of the boiler by a small amount each time.
I've considered building my own overrun feature using a mains powered relay, a microcontroller and a solid-state relay, so that when the system turns the pump on, it is actually just indicating this to a microcontroller, which will delay the turning off. Like so many similar ideas, it's in my head rather than built...
Ewan
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message

stops
a
feature
so.
I too have a design in my head but it only requires one power diode (rectifier), one resistor, one electrolytic capacitor and one relay.
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A microcontroller just to give you a 2 minute delay - bit of an overkill isn't it?

--
geoff

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geoff wrote:

Cheap enough these days, and about 30 seconds of programming effort. Why ponce about with 555 timers (flaky at long delays) ?
Steve·
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Low power 555's handle minutes without problems, but this application probably only really needs around 10 seconds, and it doesn't need to be accurate.
--
Andrew Gabriel

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The commercial ones use shift registers (40154?)
There is no such thing as 30 seconds of programming
--
geoff

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On Sun, 04 Jan 2004 23:35:57 +0000, Andrew Gabriel wrote:

Wouldn't a slow release relay/contactor be suitable?
--
Ed Sirett - Property maintainer and registered gas fitter.
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You can buy variable delay relays from RS etc, but they're far more expensive than making your own.
--
*I have a degree in liberal arts -- do you want fries with that

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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On Tue, 06 Jan 2004 00:04:07 +0000 (GMT), Dave Plowman

I used a multifunction electronic staircase timer (RS 277-3520) - £18; for a similar application.
It seemed to me that by the time I had bought the bits, put them together, got a small power supply, put the whole lot in a box, it would approach this on parts before considering the time taken.
.andy
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I was basing my view on the fact that anyone capable of making such a thing would very probably have many of the parts needed simply lying around waiting to be used. Or perhaps that's only me. ;-)
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*I will always cherish the initial misconceptions I had about you

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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On Tue, 06 Jan 2004 11:11:20 +0000 (GMT), Dave Plowman

Fair point. Yes I know what you mean. I have boxes of components where I have to look up the part number to remember what they are.
.andy
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I do hope you've kept some old RS catalogues from the days when they used to print their part number on ICs etc, I have.
--
geoff

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I was surprised that they are still printing the paper catalogue, but they do. I had a package with half a tree in it from them the other day.
Regarding legends on ICs, this reminds me of my early career, designing control systems for mobile radio applications using some of the early microprocessors. The only suitable options for program storage were bipolar proms, which at the time cost £35 each for a 1kbyte one. Since these weren't eraseable, it did mean that you checked your code. Even so, we got through hundreds of them...
For the interface logic, it was necessary to vendor select because some vendors components, although meant to be identical, were made by a different prduction process slightly and the radiated RF from them could vary considerably.
There were interesting tales here, because as design engineers for the product, we held the authority on which vendors were approved and which were not.
One vendor, who shall remain nameless, but whose logo is a bat wing symbol, had one of the cleanest ranges, RF-wise. Unfortunately, in the countries of the middle east where a lot of the products went, that particular vendor at the time, was very definitely persona non grata. To get around this, we sourced the self same components from RS which had had the logo removed and the RS one on there instead.
Another vendor shot himself thoroughly in the foot by the way that he operated. The smarter reps would come in and visit the engineers and discuss their projects as well as introducing new products. They brought data books, of course, and the really smart ones would ask about the "homers" that engineers might be doing. Samples of suitable components would then appear in the post or on the following visit. Occasionally, they would invite a group out for a pub lunch which was always appreciated.
One particular rep really hadn't checked into how the game was played. He had made numerous visits and a few of his products had been designed in. However on one particular occasion he showed up just before lunch with none of the items promised previously and then made a thing about having to rush off to take the buyer for lunch. By the time they returned, the few qualified items had been deleted from the approved list. Despite the later protestations of the buyer, the vendor never did sell anything into this product range.....
.andy
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I *think* the website will give details of any obsolete part number - or it has for those I've tried. And the fast find part of the cat does as well - although of course I've not done an exhaustive test.
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Maplin used to do a chip designed for car heated rear windows etc on which you could set the time from a few seconds to a day or so with just one R & C. It had enough drive current capability for a meaty relay, and could either toggle on or off, or on at power up. Much less susceptible to interference on the supply than a 555. Cheap, too, and I bought a load of them as it's an easy answer to many problems. One of them provides the 14 hour timer for my Ni-Cad charging area.
--
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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geoff wrote:

Yes, unless microcontrollers are already being designed into the system.
My house has 4 zones + DHW, yet there is just one thermostat. The zones must be controlled by flicking switches behind a kitchen unit...! I think whoever installed it was good at plumbing but knew nothing about usability.
I'm currently working on controlling these in a more convenient manner, using one or more PICs.
Ewan
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You should really be installing a programmable thermostat in each zone. Then each zone can be timed separately AND will hold better temperatures.
Christian.
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Aah - so it's not just to give a 2 min delay then, I'll let you off
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geoff

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In an earlier contribution to this discussion,

I don't know whether the boiler has a built-in pump over-run facility - but being 1984 vintage, probably doesn't.
In think that in your position, I would implement my own - using a mains relay and a pipe stat. Connect the coil of the relay to the boiler switched live. Connect the relay contacts to a permanent live and to the pump. Connect the pipe stat contacts in parallel with the relay contacts. Install the pipe stat on the boiler flow pipe and set it a similar temperature to the boiler's own stat (a bit of experimentation may be required!)
The pump will then run whenever the boiler is firing *and* whenever the boiler outlet temperature is above the pipe stat setting. This is, in effect, what a built-in over-run stat would do - and is better than an arbitrary time delay.
--
Cheers,
Set Square
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