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I have a EP2000 Potterton Programmer which has developed a continuous humming noise. The central heating light flickers, whilst the hot water light remains stable. Can you advise the possible cause for this humming noise which has just developed. The programmer is only 2 yrs old. Thank you.

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  • johnwgarrett Feb 10, 2010

    Typically, when I went round to investigate the humming noise it did not happen. However, thanks for your suggestion to the problem. Should it occur again I will attempt to use your advice. Thank you.



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Hi there,

Well first of all you can please follow the below steps -
1. Set the programmer to CH on, HW off.
2. Turn the room thermostat right down. 
3. Measure the voltage between N and the terminal marked SwL on the mains terminal block of the boiler (should be AC 0V). 
4. Continue to measure this voltage and turn the room thermostat right up (there may be an audible click at the thermostat as it changes state). As the thermostat demands heat, the SwL voltage at the boiler should switch to AC 240V. 
5. Set programmer to CH off, HW on and repeat 2 to 4 with HW thermostat.
Please post comments for more help or information.....

Good Luck!!


Posted on Feb 03, 2010


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Hi and welcome to FixYa, I am Kelly

When everything but the heat works there are 2 common components that fail. The high voltge capacitor or the high voltage diode. In rare cases the magnetron fails because the oscillator in the top of the magnetron sticks. When the oscillator sticks the magnetron makes a LOUD humming sound and you do not get heat. However.... a open diode or shorted capacitor will make the exact same sound briefly before the main in line / internal fuse fails.

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