Three companies have tried to fix it. It still isn't fixed.
It sounds like you've paid for visits that each found something, changed something, and left the same fault behind. That's wearing, and it's fair to be wary of a fourth.
Before the next visit
- Gather what the last ones left: reports, readings, and what was replaced. The pattern across them often says more than any one visit.
- Note when the fault appears. At a time of day, in wet weather, when a zone is in use, after a power cut: a fault that comes and goes follows a condition.
- Ask for a reading, not a part swap. A fault is found by measuring and narrowing down until the reading changes, not by replacing parts until the panel clears.
- Ask for the diagnosis to be priced on its own, separately from any repair.
Questions for the next company through the door
- How will you find it, rather than guess at it?
- What will you measure, and what did it read last time?
- If you don't find it, what are we paying for?
If that doesn't settle it
You might expect us to say the last three got it wrong. They may each have fixed a real fault; a fault that comes and goes can hide behind others, and that makes it hard for anyone.
Would you be opposed to sending what the last visits left before anyone else comes out?