Combi boiler external flue

[Bubble80]

Most boring thread title ever. But...water pressure on my boiler dropped, had plumber in to check for leaks, couldn't find any, despite looking under every floorboard. We have two heaters that were new looking, so when we had new heating installed we left them. They have plastic piping, the rest is copper, so assumed leak with them. May still be them and am getting a quite to copper pipe them.

Anyway, I refilled the system and it's been fine for two days. I notice a drip coming from the outside flue. It's not constant, in fact it's barely noticeable. It's still under warrenty. Plumber did check the boiler and all looked fine. Of course it didn't leak when he was here! Only today.

Any ideas? Should I get them back? Is the the expansion module? Pressure release valve?

I would get them back. PigletJohn is your best bet for advice here though.

the flue of a condensing boiler will drip a bit in winter. It's just condensation. There should not be much except when you are running a bath and the fan is running fast, as the flue should be tilted slightly so it runs back into the boiler where there is a drain.

btw try to catch it in a big plant pot or something as it is slightly acidic, like tomato juice, and will damage concrete surfaces. I have a wall basket of heather under mine.

if you had water coming from the small metal pipe close to the flue, that would be your pressure relieve valve passing. Common and a straightforward boiler repair.

Look round and under all your radiators, it is probably at a valve or joint. It might be under the floor. During the heating season, leaks on radiators do not show as they are hot so evaporate away, but may leave a dirty mark.

Copper pipe is considered to look better than plastic, which is often used by amateurs as less skilled, so possibly there is a bad joint. You plumber will notice if the wrong type of plastic pipe has been used.

Hi John, thanks! I will look into that. It's right above the front door so a hanging plant would be put only option or we would have to step over a flower to get out of the house! It's def not coming out of the small pipe...I've never even noticed a small pipe. The flue is literally a tiny drip. I saw one solitary drip on the doorstep theis morning so it may be condensation.

Did it slowly drop, ie over a couple of months? I'm sure you're aware but pressure does drop a little and boilers need topping us, our last one we had to do about 4 times a year, our present one 1-2 times. I always notice the pressure is a little lower when it's really cold, so could be that it dropped a little do to that and also needing a top up.

Hi mad , yes it was over a couple of months. Last time it happened like this it was a slow leak, hence my calling the plumbers. It could be nothing.