Cost depends on what it is and whether you just need to tighten a joint
up something else trivial

--
geoff

OK, I took the inner casing panel off and it runs OK with no problem.

The drips were coming off the bottom of the heat exchanger ie about 2
inches below the igniter electrode -suggesting that a gasket might be
on the way out. Or worse still maybe the heat exchanger/burner
interface is warped??

What is odd is that the flow varies from nothing up to a steady two
drips per second. I havn't seen a pattern yet which would identify the
parameters which affect the frequency of the drips.

The only hint so far is that the drips are rare immediately after the
boiler has started up but increase when it has been running for a
couple of hours. Might this be after most of the TRV's have closed
when they are up to temperature. Here I would advise that there is a
bypass valve installed so the TRV issue might be spurious.

If it is a simple gasket issue, where do I get a gasket from? I'm in
London.