Generally speaking your boiler should have a dedicated circuit (I really refer to urban boilers on 15A/16A circuits).

I can't speak for oil-fired boilers though.

my router re-syncs the moment the burner ignites.

Something I've never read before.

On the cores, I think it is experiment - my rf knowledge in that area got pushed out of my brain some years ago

In reply to a post by camieabz:

my router re-syncs the moment the burner ignites.

Something I've never read before.

Oh, I try to be original

Not every time though otherwise I'd be back to dial-up speeds!!

In reply to a post by MrSaffron:

On the cores, I think it is experiment - my rf knowledge in that area got pushed out of my brain some years ago

Marconi invented a way of sending "wireless" messages using the same principle. Remember that?

Sounds as though you have found the actual problem.

The transformer may be in a box but there will be a piece of wire from that to the point of ignition - a great antenna! The transformer may also be operating at a lot higher than 50Hz - incoming mains is rectified and stored at 250 - 300V DC then switched with a free running oscillator which will create a whole series of frequencies in a "comb", that passes through the transformer to provide the 8kV

The ferrites are worth a try - it is a bit of a black art. You can pass the wire through or through, round the outside and through again. If you can get two of different sizes - they will have different characteristics. Fit them close to the boiler. It might also be worth fitting one one the control/thermostat cable.

Even with a balanced flue there could be an internal fan - my boiler has one.

Again, thanks for the reply.

Sounds a bit like the line output transformer principal in a proper TV

I will try the ferrites as you suggest!

Andrew said that it doesn't happen every time, so I'd guess that it's not the ignition per se, but whether it's the transformer or a fan there's an inductive load suddenly being switched in- do that at the wrong moment in the mains cycle and there'll be quite a spike.

A filter in the supply to the router might do it... I run mine from the UPS, but that might be an expensive cure if there isn't one already there!

as I understand it, in a conventional oil boiler, the oil is ignited by a spark, this spark continues until heat is detected.

it may be that over the years the spark gap has been eroded, and requires adjustment. or the heat detection need cleaning.
this may not stop the noise all together, but would make it shorter so the router may not resync.
there is also a motor to spin (distribute) the oil, check that as it starts up at the same time.

whats the noise like on an am radio?

the simple test to see if a ups would help on an adsl router is run an old usb one from a laptop while testing.
edit: but you are always better removing noise at its source

Edited by ggremlin (Tue 23-Nov-10 11:28:21)

In reply to a post by ggremlin:

as I understand it, in a conventional oil boiler, the oil is ignited by a spark, this spark continues until heat is detected.

it may be that over the years the spark gap has been eroded, and requires adjustment. or the heat detection need cleaning.
this may not stop the noise all together, but would make it shorter so the router may not resync.
there is also a motor to spin (distribute) the oil, check that as it starts up at the same time.

whats the noise like on an am radio?

Good point about an eroded spark gap. I will also check using an AM radio, my usual way of checking for thunderstorms within range!