Boiler problem - which trade to call?

I'm at a loss with our boiler at the moment. It's been acting up a lot lately. Have had it serviced annually without too much ado. We have an oil boiler and a back boiler stove both of which are connected into a Horstmann 3 zone panel (upstairs, downstairs and water). There is a switch to turn it from boiler to stove which is essentially on for boiler and off for stove. There is a separate switch to turn the whole thing off which turns the panel screen blank. What we are finding is that when this second switch is in the on position the boiler will turn on completely on its own despite the panel zones being set to off. Came home today to find the boiler operating away for who knows how long and a house like a sauna. Also, occasionally, when the water only zone is activated by way of oil boiler the rads heat up as well. Had a plumber in to service the boiler in November and he reckons all is ok with that. Spoke to an electrician who said he had come across this a few times and changing the panel had solved it in these cases. Got the panel replaced just before Christmas at a cost of €160 but it is still happening.

Would anyone have any clue where the problem actually lies and who I need to call to sort it? I have no problem paying someone to get the issue resolved but I'll go bonkers if one more tradesman comes up with a plan to sort it and leaves me hanging again. Any recommendations would be hugely appreciated also - Cork area.

Thanks in advance.

Go back to the installer, it is a complicated system but done right from Day one unlike many others including my own.

Could be an issue with the microswitch(es), assuming your system used them. We have Orkli and they have a reputation for being flakey. They look like a red box on a brass plumbing fitting, google image it.
We too had a stove and a boiler tied in the the one system and when one of the switches broke it was so confusing. To make it worse we had manual switches for choosing the zones.
Anyway, got the stove disconnected from the system as it was just too much hassle. Automated zone system and replaced the Orkli with a different brand, it's been all good since.
Where in Cork are you?