What is this thing coming out of a Heat Interface Unit and why does it leak?

Is the rusty thing made of metal?

could be a non-return valve can't really think why one should be needed there, send the council your video and tell them to look closely for the drip of water?

I am not familiar with that type of boiler but looks to me as the outlet for the pressure relief valve. Try and establish if that pipe simply goes to the outside. If so it is the PRV outlet. If it is the PRV then it should not be spitting out as any water flowing through the pipe is not under pressure even if the pipe fitting is loose. It might be blocked somewhere and as a result back filled with water.

It does look like a version of a tundish on the outlet of the PRV:

It sounds like two problems. First the PRV shouldn't be opening to put water here, second the piping around the tundish shouldn't be dripping. The second might be because the overflow is blocked, but the first suggests overpressure which is a fault.

Theo

Without knowing the exact model it is difficult to diagnose. It looks like a pipe under pressure from the fittings used.

I think Simon has the best suggestion. And ask why the engineer couldn't find anything, despite there being an obvious leak?

Could you do another video looking upwards into the boiler, please. And with a close up of the leaky bit.

At the moment, my best guess is that the leaky bit is not part of the heat interface at all. It's just been poked under the cover of the interface for neatness.

It might well be an automatic air vent. In that case, a tiny bit of water spitting out with the air may not matter much, and that might explain why the engineer thought there was nothing wrong.

To put a new AAV on might involve draining a large part of the system, so why bother?

^^ I meant interface, not boiler.

possibly, he wasn't an Engineer.

Shouldn't the PRV pipework be copper, and not plastic, so close to the boiler? Or indeed any pipework?

My MPHW tank did this - tuned out to be a faulty pressure regulator. Check the hot water pressure if you can - should be no more than 2 .5 bar or thereabouts.

Likely culprit if ion a hard water area is scale

I managed to replace mine OK, but its not for the faint hearted

Good point. Many boiler installation instruction require a minimum length of copper from the flow side. However after checking for my Intergas boiler I can't see any stipulation so seemingly not a universal requirement.

GB:

Here it is. This is the best I could do:

Theo

Tim

It is the condensate drain off. It looks like the fitting has come apart slightly. If the condensate tank wasnt full when it was checked by the Council, then it is quite possible that it was running fine when it was checked, and no leak could be seen. These have a small tank inside the boiler, the condensate comes out in one flow when the tank is full, rather than constantly dribbling out like some boilers. Its a simple procedure to take it apart and refit it correctly, and also check the outlet pipe is clear, as, if that isnt clear, it will back up and eventually turn off the boiler. It looks like it needs a good clean, something that should be done on an annual service, but one of the things that is easily ignored.

They've decided you need registration to see that. Let me try a different sharing site:

I wonder if someone has left the filling loop turned on?

Tim

Usually due to a leaking valve on the filling loop, which legally should be removed after use, but never is.

Is there really a law about removing filling loops? If so, what?

Condensate isn't normally coloured brown.

I would wager the PRV is weeping given the boiler pressure reading on the gauge.