Potterton 80E CH cycles off/on, off/on ...


Yet another Potterton 80E problem to add to the collection:
The Central Heating is firing for 10-30 seconds, then switching off, repeating this cycle ad nausaeum. We are also getting frequent lockouts when Hot water is demanded, though I'm not sure if these problems are related.
Many thanks for any ideas the group can offer.
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I had this problem with a Saunier Duvall boiler, it was down to the incoming gas pressure being too high. Once we adjusted this down it seemed to be OK.....so far !

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Iain A Gilroy wrote:

circulate water? Hot water would draw off a lot of the heat from the exchanger provided flow rate is high enough, but central heating relies on the pump to move the heat out and round, is it working well enough/system clagged up?
Velvet
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The Tapir wrote:

Sounds like a pump problem might cause both problems.
- Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at www.diyfaq.org.uk Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
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Iain A Gilroy wrote:

Similar problem here once. Annual service, guy turned up the pressure after years of no change saying it would give faster heating, etc. That led to lots of kettling so called another guy back who tweaked it back down, but he could only guess at the previous setting. It's not a modulating boiler, just a simple low/high thermostat switch.
Is gas pressure straightforward to twiddle?
Sam.
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This is a range rated burner. There is a plate on the boiler giving the pressures v kWs. Get a heating engineer not a plumber.

Yes, just look at the plate, know how to use a U gauge and know where the governor screw is.
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Yes, as long as you've got a reasonable clue about what you're doing!
The installation handbook for your boiler should have a table which shows heat output versus gas pressure. You have to: 1. decide how much heat output you need 2. connect a manometer ** to the pressure measurement point 3. tweek the governor with the burner on (and the boiler fully warmed up) to give the correct pressure - as measured by the manometer
As a cross-check, you can time your gas meter pointer going round when the boiler (but no other gas appliance) is running - to make sure that it is consuming gas a rate commensurate with the desired settings.
** You can make a manometer out of a strip of wood, some plastic tube - filled with water, bent into a U shape and fixed to the wood, and a piece of graph paper between the tube and the wood to measure the difference in water height between the two sides of the U
As an example, my boiler has a heat input of 23.7 Kw (80,900 BthU/Hr) at a gas pressure of 4.0 inches of water (10 millibars). Since it's about 75% efficient, its heat output under these conditions will be about 17.8 Kw (60,700 BthU/Hr). The gas consumption would have to be calculated from the calorific value (as stated on the Gas Bill) - in order to convert 23.7 Kw into cu.ft/min - or whatever it is that gas meters measure these days.
Roger
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On Fri, 14 Nov 2003 17:17:22 +0000, Roger Mills wrote:

afterwards to chekc you have not left it leaking.
Sounds like you have Profile 80e. That would be a 24kW boiler so you would have a very large house if it needed that sort of heating.
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It's actually a Baxi Solo 70/4 PF - which is now 10 or 12 years old. The figures I quoted were for the intermediate setting. Its max input is 26.6 Kw (90,900 BThU/Hr) and its max output 20.5 Kw (70,000 BThU/Hr) - hence the "70" designation.
When it was first installed, I was intending to extend my house (which I have subsequently done twice!) and wanted to allow scope for extending the heating system to match.
Roger
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I had a go with my back boiler to cut down noise and short cycling.
I didn't have a manometer, just tried to stay on the safe side and make sure ignition was ok.
The result was outstanding, short cycling gone and noise down.
I'll now duck in case I've done something extremely bad,
mike r
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