Possibly or a motor having trouble starting.

I suggest freezer as a fridge would be more frequent and if you have a dual compressor (one each) fridge freezer it is possible. Plenty of others including a neighbour on a wall backing on.

At 90 degrees no issue with normal noise but a burst could cause it. Is the transformer a tap switching version? So as the incoming voltage drops/rises it will step up/down?

See if you can get a few more occurrences and measure the mains before and after.

Is the transformer a tap switching version?

I don't know if you are following on from my question about the transformer, but I was referring to whatever is providing the 230V supply from the 11kV feed. I doubt if the OP knows anything about it.

Goodness knows what could be going on in the cabinet holding that.

In reply to a post by RobertoS:

Where's the transformer?

About 75 feet from the phone line, at the top of a pole.

Edited by Andrew_W (Sat 06-Nov-10 14:19:13)

In reply to a post by MHC:

Possibly or a motor having trouble starting.

I suggest freezer as a fridge would be more frequent and if you have a dual compressor (one each) fridge freezer it is possible. Plenty of others including a neighbour on a wall backing on.

At 90 degrees no issue with normal noise but a burst could cause it. Is the transformer a tap switching version? So as the incoming voltage drops/rises it will step up/down?

See if you can get a few more occurrences and measure the mains before and after.

The transformer is so old I think it was one of Faraday's first attempts One of those oil filled ones covered in rust. The supply company said they would replace it within 2 years, 10 years ago!

Also, I live in the middle of nowhere so no neighbours.

In reply to a post by RobertoS:

I doubt if the OP knows anything about it.

Are you suggesting I don't know what I'm talking about?

'Twas posted before you said anything about it. In case MHC was meaning the power supply to the router.

Fair comment!

Resurrecting this thread, I have established that my problem is my own central heating boiler!

The electrical installation is only 6 months old, the boiler is oil fired so my spike is coming from either the boiler thermostat, the fan motor starting in the oil burner or the piezoelectric spark that ignites the oil.

I have checked the boiler earthing, fitted a mains filter to the router power supply, my incoming phone line and router are on opposite sides of the house to the boiler. This has tripped my router three times in the last two hours so is obviously getting worse. It doesn't always happen when the boiler fires up, presumably dependant upon when it happens in the mains cycle.

Any bright suggestions please as to the most likely cause. Suppressing the piezoelectric, not a good idea with the forthcoming cold weather

Have you filtered the boiler supply? It may have to be a ferrite on the cable.

However, it may not be transmitted through the cable but radiated and picked up by the router or last length of cable.

The boiler will ignite in a certain sequence: thermostat, water pump, oil pump, extractor fan, ignition ... can you monitor it very closely to see at what stage it happens?

You mention Piezo - is it? It could actually be a very high voltage spark and the circuit to generate that will have some nasty radiation characteristics.

In reply to a post by MHC:

Have you filtered the boiler supply? It may have to be a ferrite on the cable.

However, it may not be transmitted through the cable but radiated and picked up by the router or last length of cable.

The boiler will ignite in a certain sequence: thermostat, water pump, oil pump, extractor fan, ignition ... can you monitor it very closely to see at what stage it happens?

You mention Piezo - is it? It could actually be a very high voltage spark and the circuit to generate that will have some nasty radiation characteristics.

Thanks for your learned response

Last things first, looking in the book of words it mentions an ignition transformer with an output of 8kV, not piezo as I thought. Suppressing that would be difficult although it is in a steel box and of course the whole boiler is in a steel case.

The water pump is upstairs and there is no extractor fan (balanced flue) and I have checked, my router re-syncs the moment the burner ignites.

As I said, this has only recently started to be a problem. The boiler is 8 years old and serviced annually but was moved about 6 months ago to a new position in the house and rewired to a new electrical circuit. My router now shares that new circuit so I will try connecting it to the old house wiring to see if that offers any form of isolation.

When you refer to a ferrite on the boiler cable, would a clip on type be adequate like these?