Thanks for the replies - I had stopped checking after a week, hence the late follow-up, but in case anyone wants to know how I got on:
- I put down plenty on masking tape and penciled on where to drill
- Drilled through with an HSS bit (didn't seem to be making progress with the pilot drill...
I have bought a Steel\Enamel bath:
http://www.kaldewei.com/en/produkte/baden/form.php?active=eig&segment=am&form=77&format=&me=mm&type=2
The plumber we've been speaking to doesn't think drilling a tap hole into it would be wise. Does he speak the truth? We would've got the model with...
Setup:
Potterton Housewarmer 45 back-boiler, about 6 years old; 6 rads (old rubbish ones - just sheets of metal with the pipe going round in a loop, i.e. no water in the rads themselves, but should be beside the point for this problem...).
When the boiler ignites, every now and again (maybe...