Electrical Problem

[herebriefly]

Attended a property this evening where the 3amp Central Heating fuse keeps blowing.

The custard had another company who changed the fuse yesterday.... and left quick smart.

So, i've gone in after picking the van up from the garage as its had a new cam belt today. So... no tools on the van apart from what I carry in my work trousers.

Basically... i've replaced fuse and fired up the hot water on the timer. (S plan sealed system on a Potty Profile) and all fine. (Personally I was thinking Pump).

So, put on the heating on the timer and all OK. Go to room stat and create a call for heat and BANG... fuse blows. I check the 2 port for possible leaks and all seems ok. I had a like for like Honeywell room stat
in the glove box and just thought i'd try it. (Never had a room stat blow fuses before though). Tried new stat and all is fine.

So... can the live go straight to neutral through the anticipator as thats the only reason I can think of as to why a room stat could blow the 3 amp fuse. Wiring to the old stat seemed in good order but thats counts for nothing really, does it! The old stat is still at the property at the mo as I should have brought it home to test it but was in a hurry. Ill get the old stat Monday and test it, but just was curious.

Anyone had this occurence as in over 20 years of being gas / heating man i've never came across it.

David.

 

[rojaca]

Had exactly same two weeks ago. Yes had a dead short live to neutral across the anticipator. Had some marking around the circuit board
What threw me was when I was doing my electrical checks, I'd asked the customer where the room stat was.
"we'll go don't worry, do you want it turning up?"
"yes please, right the way up if you can"
planks had turned it up to 18 degrees which wasn't enough to call at the time, which led me on a right merry goose chase.