Pulsa Coil A class boost not working

When I push the boost button it doesn't switch on. I have check the "on peak" immersion and get 18ohms so I believe this is ok. I have checked that I have 240v in to the "on peak" power relay and I do but I have nothing on the output from the relay. I suspected a burn out relay as usual. I tried the "Off Peak" Power relay in the place of the "on peak" relay and when I power up the unit with only the "off peak" relay in the "on peak" relay position the relay switches open and closed lots of time and you can see sparking inside the relay and the unit shuts down. Any help Mike or others ????? Please. Brian

Look in the parts list.
There is another very small push in relay with very fragile pins.
You have been warned
Mike
MGC/H2O
Norwich
Norfolk

Thanks Mike, I have tried replacing this (Relay 3) still no change to symptons ?? Any other suggestions ?

Cheers

Brian

Is the unit hot when you are trying the boost?

Mike thanks for your help. I have solved the problem, so I post this in case it helps others.

From the earlier post you will see that I had presumed that the off peak relay was OK as the water was heating overnight as it should and when I put that off peak relay in the On peak it arc'ed internally. I was leaving the off peak relay location empty.

I then decided to replaced both relays and it now works fine. I am not 100% sure why but it seems that the two relays either work in conjunction with eachother so you need a relay in both locations to test them or the off peak relay was defective in some way and the system was using the boost immersion on off peak but when you try to boost it tries to shut the off peak circuit but couldn't due to the defective relay (it is not clear that the unit does this from the circuit diagram but it may be a feature in the chip on the PCB). Moral of the story is that if you are getting bizzare symptons then replace both relays to test the unit. you can still then find out which one is defective and keep the other as a spare as they tend to get pretty often.

Hope this helps

Brian