CH coming on with HW even though set off on programmer

We have an old Stelrad Ideal WLX boiler which has been working perfectly and is regularly serviced.

We are now having a problem with the radiators heating up when the programmer switches on the hot water. The programmer is set to keep the central heating off all of the time and only activate the hot water function (programmer is a SUNVIC 207 Select XL).

Obviously we are in the middle of a heatwave and to say that its inconvenient to find the radiators churning out heat just because you want a bath is an understatement!

What I should also mention is that we have recently had the electricity off and also the mains feed for water off for work to be done on our kitchen. The boiler was however turned off while the water was off.

I have taken the programmer off and re-programmed it about 6 times.

Can anyone help? Not sure whether the action of taking the water on and then putting it back on full blast may have damaged the diverter or diaphragm in the boiler?

Is the solution to the problem as simple as the cause seems to be? I know that any engineer that we get out is going to recommend replacing the boiler due to its age but having just forked out for the kitchen I'm a few beans off being able to do that just now!

Help much appreciated.

check your motorised valve

Have just had a look at the motorised valve and now have a recollection of one of my children fiddling with it on Sunday morning while I was getting towels out of the airing cupboard.

The valve is a Sunvic UniShare SDM 1901 with a thumbwheel - the problem is I have no idea what position the thumbwheel should be in?

Any suggestions - happy to give anything a go - desperate for a bath but melting in the heat with the rads on!