Potterton Promax 18 SL Very Loud Intermittent Noise

22 Oct 2014
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United Kingdom
My Potterton Promax 18SL boiler is making very loud intermittent cyclical vibrating noises lasting for 10's for anything up to 1 minute. It sounds like it could be a fan of some kind but I don't understand why it would be only making noises intermittently.

Adjusting the c/h thermostats or turning off the hot water via the programmer mostly make it stop until the next time.

It also only does this during the autumn/winter months when the programmer and c/h thermostats are set for the heating to be on. Not during the spring/summer when only hot water is on.

This is the second year running it has done this and the boiler engineer could not identify the problem when it was serviced last year.

The central heating system is on a 3 year old house, has wet UFH downstairs, radiators upstairs (with TRV's). The cylinder is a an indirect unvented Megaflow 201i.

It appears to be random when the system makes the noise, it could be when the heating is on or water, or both at the same time, and at different times of the day.

The megaflow temperature settings are set to their minimum settings, and the hot water temperature varies between 60-72 degrees, depending on how long the water has been on. The temperature thermostat does appear to be cutting out as expected when the temperature is at the required temperature, but have noticed on occasions that the hot water pump is still running when the water temperature is ~70 degrees and the upstairs heating which is on the same pump is off. Even so I'm not sure how hot the water should get when on the minimum setting and why/if this could be causing the boiler noise.

The megaflow expansion bubble in the has been replenished and there is no dripping from the T&P valve. The megaflow system also has an external expansion tank.

Any ideas anyone?

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Hi I realise this is an old post but did you find out the cause of the vibrating noise because my Potterton is doing exactly the same

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