I have a Vaillant turbomax 824E plus which has no display and is not switching on its dead,removed control box covers and tested elecs Iv got 240 to mains block into boiler and external elecs are fine,when i turn on the boiler I still get nothing on display no lights nothing,but I then get live to pump, fan,transformer but the neutrals are also showing live on all three,I have disconected all components including plug in clock and display module and there is still live to all neutral pins on board

sparkwort, February 2011

thanks for reply carefree,but maybe didnt explain my testing,I actually had 240v at boiler terminal block across L and N and had also already ascertained fused switched supply was good.It was only on actuall turning boiler on at on/off switch on boiler that problems arose

sparkwort, February 2011

May I respectfully suggest your testing methods may be a bit awry?
If you have 220-240v at the mains block, you can only establish this correctly testing between L&N. If, as you say however, your neutrals are also live, you cannot establish 220-240v between L&N as you are measuring potential difference and your reading therefore would be 0v

Do not rely on L&E or N&E to give you readings, this alone cannot determine polarity.

Please turn the thing off (for your own safety) and get someone in who knows what they are testing.

Carefree, February 2011