Danfoss heating controller dead?

Our central heating stopped working a couple of days ago. Around the same time there was a strange smell in the house which I thought was smelled like some sort of electrical burnout, though my partner disputes that.

The boiler has still got it's pilot light lit but the Danfoss 102E5 controller doesn't appear to be working.

Although the controller display looks normal, the red light that shows that the heating/water is on never comes on any more, either when trying to activate the system manually or via the timer settings.

The Danfoss controller should be protected by a 3A fuse, but when I checked the supply, there was a 13A fuse in place that had failed. Replacing the fuse doesn't lead to any further failures but nor does the controller work again.

I was wondering if anyone is familiar with these Danfoss units and whether if the red light no longer comes on it means that the unit has failed?

Does this sort of thing just happen out of the blue? We've had this controller for years with no issues, but I guess the incorrect fuse being in place could have led to the unit being overloaded.

Replace the 13amp fuse with a 3 amp 1st, then get another 102E5 they still are available so it is a straight swap. It failed because it developed a fault and the fuse did nothing to protect it or anything else, very bad whoever did it.

Thanks for the advice.

I found a cheap 102E7 on ebay and the seller assured me it was in good working condition.

I changed the fuse for a 3A, installed the new unit and the red light was coming on again.

Unfortunately now the boiler won't fire up.

I initially thought the problem was the pilot light as this had gone out but I relit it and the boiler still won't come alive though the pump seems to be whirring away ok.

The boiler is an ancient honeywell glowworm space saver mkII and it's electric supply (also rated at 3A) appears to be connected to the same plug that the programmer is.

Could it be that the 13A fuse in place of the 3A has also lead something blowing in the boiler?

Is there anything else I can try or is it time to call in a professional?

Thanks

I'm no heating engineer, but logically it sounds like something else has shorted taking out the controller with it or vice versa. Maybe room thermostat, HW tank thermostat, a motorised valve, wiring etc.

If you are confident using a multimeter and working around 240V AC safely, then have a read up (in the FAQs here or elsewhere) how these things are wired up together then get testing for shorts, continuity and that the various devices are calling for the boiler to fire as expected. If not then it's probably time for a professional - a live mains AC installation is not the place to be learning how to use a multimeter / circuit tester, the simplest mistake can have dire consequences

Thanks - I don't have the kit and am a bit of a dunce when it comes to electronics so I think I'll leave it to somebody qualified.

One thing I did notice was that when I opened up the electrical controls drawer to see if there was anything obvious amiss, I noticed quite a lot of mouse droppings inside (we've been having a mouse problem of late).

I noticed that the transformer was covered in mouse droppings and that on the front plate of the drawer next to the transformer there is a scorch mark on the metal.

Did a mouse do one poo too many and short out the transformer? That's my theory until a plumber tells me I'm losing it anyway

I'll report back with what the professional verdict is...

Entirely possible that the mice have damaged something. They do have a tendency to chew through wires and the like.

And just by coincidence another thread popped up on here today about mouse damage in a boiler: //www.diynot.com/forums/plumbing/mice-in-boiler.366605/

Well in the end it was the transformer.

By a stroke of luck a local shop had the part for £70, a quick swap and all is working again