Potty Potterton Performa 80

Its started playing up again. A 3 year old boiler and i replaced the PCB last year.

Now when the DHW is requested it sends the heat to the rads. I have changed the diaphrams in the diverter valve and this doesnt seem to have made any difference.

When the tap is turned on both microswitches are pushed closed is this normal?

Central heating seems to run fine just got no hot water now.

Could it be the heat exchanger? if so how would you remove this as i cannot see any unions is it possible to descale with a proprietory descaler if so which is brand recommended?

can i descale with it still in place put putting into radiator circuit?

Any help would be appreciated. thanks

close the isolation valves underneath. if it overheats then its blocked.

2 screws to remove and yes both microswitches shoould open on HW

edit. noticed you said diaphrams, these wouldnt make much difference, so it could still be a seal inside the DV

thanks for the advice i closed off CH valves and ran the taps hot water and after 15 seconds reached 80 degrees and turned burner off to cool down. I assume this is what is meant by overheating.

Is it possible to descale the heat exchanger?

What sort of product would be best to use?

How much "should" it cost to have a plumber come out and do it?

the water actually got hot then before it overheated?

i personally like to use 'Ferroquest' pretty strong stuff. can usually drain clean and refill within an hour maybe hour and half. plus chemicals £20...wouldnt have thought more than £100 TBH.

last one i done to a vaillant we only charged £75.

yes hot water came out of taps rather than go into CH as they were closed off thanks for the info. Can anyone recommend someone who will come to Portsmouth to carry out the descale? thanks