Pump won't stop when cylinder stat set to 60c

17 Sep 2010
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United Kingdom
Hi all, I hope someone can help.
Recently my pump keeps running if cylinder stat set to 60c. If I lower stat to 55c it operates normally. At 60c the boiler shuts off when temp reached but not pump. Pipes to & from cylinder are hot as is valve to cylinder. I thought maybe cylinder stat was at fault but after changing that same problem exists.
Two things changed this summer; perhaps they're to blame. The cylinder has a foam shell ( which is cut away for the stat) and I added a jacket to it this summer to try and cut bills and carbon footprint etc.
Also my fiancé painted the pipes in the cupboard, though leaving pump and other brass alone. She did paint the plastic boxes of the valves.
Any ideas? Thanks so much for reading.
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what boiler have you got? , some boilers have a pump overun, which means the pump will run after the boiler has shut down to disperse heat from the heat exchanger
The boiler is a Potterton Prima F the i in Prima is a 1 with a dot on top like Pr1maF. It's set on 3. It goes from 0 to 5 then max.
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How high shall I set boiler? I have a micro bore CH system and last winter lots of hot drips came into the expansion tank warming the water in it. I have a small cottage w/ 7 rads. CH pipes never been power flushed etc. Pump is set to 3. What do you suggest for boiler setting and pump speed? Thanks.
1 on the boiler is 55C and Max is 82C, so 3 will be about 65C, which is probably not high enough to heat the cylinder water to 60. In any case cylinder thermostats are not very accurate, so "60" may be more. Try setting the boiler stat to 4. In the winter you should set the boiler to Max and leave the cylinder and room thermostats to turn it on and off.

As for the pump speed, with seven rads you should be able to run with it set to 2. The test is if the furthest rad from the boiler gets hot enough.
Can't thank you enough. Set boiler to 4, pump to 2. Pump finally shut off! I found an old pipe thermometer which I put on tank next to stat which said 53c on a stat setting of 60c. So one is wrong, but now have enough hot water for two showers or more where as when stat was set at 55c we only got one shower (we have a shower pump). Thanks again. I don't have much expertise to offer but if I see a question on this sight I can answer I'll try and spread the help along. Cheers

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