You're asking the wrong question!
I'm not an electrician, or a plumber, but I do know the law!
Don't try to fix it yourself - electrics can be dodgy, but more importantly, the insurance company should be fixing it!
They appointed the engineers who came. The engineers caused the problem (I'm assuming these electrical control problems did not exist before they came??), so the insurance company should arrange to have it put right.
The fact that the cover does not include electrics is irrelevant. If the 1st engineer messed with the electrics when wiring in the new valve, or in any other way, then liability is with the insurance company.
However, as soon as you fiddle with it yourself, however well-intentioned or well-advised, this liability ends!
Get onto the insurance company and INSIST they put right the problems they caused!
I totally agree too, mike raises a very good and valid point
Matt