Potterton Promax 12 SL boiler intermittent

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Hi, I’m seeking some advice on a problem that’s occurred with my Potterton Promax 12 SL boiler, the problem is intermittent. It comes on in the morning for a few hours. Then when it’s up to temperature it goes off & won’t come back on till the next day. It doesn’t come on in the evening or for a second time in the same day. Even when I try to manually or advance the central heating boiler through the Siemens RWB29 wall controller or wall thermostat it doesn’t fire up. It shows no lights on the boiler or allows me reset it. I appreciate any advice to resolve this problem.

many thanks
Richy
 
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CBW

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Sounds like a stuck motorised valve - have you got a 2 port or 3 port valve? If you’re unsure post a photo of your cylinder cupboard.
 
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Thanks for your swift reply, Chris. Hopefully these photos help. It’s a a 3 way valve.
 

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post pics of your programmer and room thermostat as well please
 
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Here’s a few photos of the controller, which is showing the CH & HW is on. Also the room thermostat & some of the boiler cover & cover off. The controller is on but no lights to the boiler in the garage. Thanks
 

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CBW

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Turn off the power to the programmer by the fused connection unit switch, leave 5 minutes and turn it back on, see if it kicks in then.
 
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Thanks, I’ve turned the power off to the controller & it’s powered down. I’ll give that 5 minutes.
 

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Whilst it’s off, have a look at the 3 port valve, it should go from H to W.
 
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I’ve turned the power back onto the controller after 5 minutes & no improvement. No power to the boiler. When I turned the power off the 3 way valve went to Water-W & when I switched it back on it returned to Heating-H.
 
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Thanks for the advice, that’s done the trick. 5 minutes after turning the power back on the boiler fired up. I’ve tested it on the thermostat, manually & automatically on the controller. Thank you very much for your swift advice, guys. It’s done the trick.
 

CBW

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It’s done the trick for now, but will likely fail again.
 
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I appreciate I’ve only temporarily solved the symptoms & not necessarily the cause. What’s your advice on a permanent fix?
 

CBW

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Sounds like it could be the 3 port, which if it is, I’d recommend a new head.
 
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So change the mid position actuator out?
 

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CBW

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Sounds the likely culprit, although one of the more experienced pro’s might say otherwise.
 

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