I’ve got a combi wall mounted boiler that has a copper waste pipe thru’ an external wall. I’ve noticed recently that it is dripping water from this pipe occasionally and probably only when the boiler is in use. It’s not a lot, just dripping, but it’s definitely not continuous drip. Don’t think the water comming out is hot either. Other than this the boiler appears to be working fine .Is this something I should be worried about?

Sounds like the condensate pipe. If it’s the condensate running back inside the house then collect it in the first instance and solve the problem, so it’s routed outside as it’s mildly corrosive. Could also be rain from outside running back along the pipe if it’s near-horizontal.

Thanx b biker. The water is running out of the wastepipe outside so isn’t causing a problem just wondered if there was a fault?

Depends whether you have an condensing boiler, how old is it? Condensate pipes are usually plastic as they’re not high pressure and the contents just drips out under gravity. Most combi boilers also have a pressure blow off valve which connects to a 15mm copper pipe. As the name implies if the pressure of the water in the boiler gets too high it shoots out of the valve and off through the pipe instead of the boiler going bang.

You can terminate the condensate into internal waste plumbing, which is handy as it stops it freezing. The blow off valve pipe definitely doesn’t want to be terminated inside.

If it’s only leaking when central heating is on it will be the expansion vessel that requires recharging with air. When boiler is cool pressure gauge will probably read 1-2bar, with heating on it will go upto around 3 bar where it will start dripping from pressure relief pipe as the safety valve opens. It needs someone that knows what they are doing and a footpump to resolve.

Thanx Yorkshire Pud will contact Brit Gas