Chaffoteaux MX2 30FF no hot water when heating on

[angip]

Have been trying to get to the bottom of this for a while. Have had the problem since replacing the PCB to try and get round another issue with having to press Reset after flame detection failure. I have replaced the 3-way-valve, as at one point I could only get intermittent hot water even with the heating off. Since replacing the 3-way-valve, I am now back in the situation that I cannot get hot water if the heating has been on, unless I power off the boiler and back on, with the heating controls all off. Going mad with frustration and about to move house, so really want to get to the bottom of it or I will be having to replace the boiler for the new owner. This is the procedure I am following to test.....

Start point: my hot water works OK with central heating controls off, ie knob turned off on boiler, thermostat on boiler set to permanently no heating.

Turn heating on with the knob and thermostat on the boiler, and turn on room thermostat. Turn on hot water and it runs cold. If I then turn heating off with thermostat on wall and turn hot water on, the hot water goes down the CH pipe and the tap itself runs cold.

If I then turn hot water knob off on boiler and turn hot water on, same problem - hot water goes down CH pipe, tap runs cold.

If I then switch off the boiler with the power switch on the front, wait 5 mins and then turn it back on, turn on hot water and it works.

Can anyone tell me what might be wrong?

Many thanks for your help.

 

[angip]

OK, so as I wrote my post, I could already see the obvious answer - change the PCB board. I still had the original board, so I changed it back. It now works with heating and hot water as normal. So much for the new PCB!

I noticed the brown box "transformer"? on the board was hot when I took out the old board, and it had been making a whining noise in operation. So I am guessing that's the faulty bit.

Will see how it goes over the next few days. Please tell me this is solved now!