Have you got a normal boiler (not a combi/condensing). If so it’s probably the flow control valve (three way motorised valve) that’s sticking.
It's not a combi or anything fancy. It's been in the house since we moved in, 22 years ago. I wouldn't have the first clue how to unstick the flow control valve though.
As long as it's not an emergency plumber you may well save more money than the call out costs if you get it fixed now.
We've budgeted for a new boiler, so might just take the plunge with that in the new year. There are only the two of us now, and we are coping quite well.
Thanks for comments though.