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What is this bit that's leaking? (Baxi)

rar4s

rar4s

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Hi, guys. I have a Baxi backboiler setup, pretty old. There is a piece on the side wall of the fire/boiler with extensive corrosion or deposits, and a drip leak. Floorboard beneath are extremely wet, may have been going some time. Is it some kind of drainage point, what is it for? Dare I try to tighten that various parts of this component, or does it look like it will snap off?

Genuine question: could I just cake it in silicone and buy myself a year or two?



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Get a wire brush and clean it up to have a proper look but it does look like a male coupler into a 3/4" adapting tee. The tee may have been used previously as a drain off or a fill point, who knows.

No - silicone will not work for any length of time. If you could get it dry then a self amalgamating tape may work but who knows for how long. If the pipe is under any real pressure then the only thing that will really work long term is to replace the fitting.
 
Personally I would be more concerned about the wiring. :eek:

Screenshot 2025-11-24 131119.jpg


A leak is troublesome but unlikely to cause injury... or worse.
 
its an old fashioned safety valve from the 60/70`s under all that crude are relief holes it can be taken out and plugged off as they are not required anymore .
we used to just cover stuff up and just snatch them . Although the tee is 22mm (or 3/4) the valves came in either 1/2 inch or 3/4 .
There is a spring under that end cap
 
Here it is a bit cleaned up. The drip is still present, although I want to say it has slowed down but I must be imagining it as the cleaning couldn't have done that?

Anyway, do we think tightening the end cap is a safe move, it's not going to just fall to pieces? It sounds like removing the whole thing will be OK, but I'll have to drain the system and would rather avoid it. Is it maybe just this spring-loaded safety valve getting a bit relaxed over time?



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rar4s said:
Here it is a bit cleaned up. The drip is still present, although I want to say it has slowed down but I must be imagining it as the cleaning couldn't have done that?

Anyway, do we think tightening the end cap is a safe move, it's not going to just fall to pieces? It sounds like removing the whole thing will be OK, but I'll have to drain the system and would rather avoid it. Is it maybe just this spring-loaded safety valve getting a bit relaxed over time?



View attachment 400668
Click to expand...
Before you try just tightening the end cap you need to see where the leak is coming from. If it's from the end cap then tightening might work. If it's from the holes, tightening the end cap won't make any difference and indicates, as you suggest, that the safety valve is leaking slightly due to a weakened spring. If that's the case then there is no alternative but to remove it and replace with a new one or, as suggested, just put a cap or plug in its place.
 
Thanks, everyone. By the pipe size I can trace this upstairs to either the pipe that takes the cold header water down to the boiler, or one labeled "hot water expansion" which comes up, T's off the top of the hot water cylinder, and then carries on up to attic (presumably back into the header tank?

Do we know which it must be? Neither can be shut off easily so it will be a bit of fun draining it.

EDIT: I take that back - these two pipes go into the ceiling and aren't seen above, so I assume go into the bottom of the hot water tank somewhere (currently obscured by a lot of stuff) ?

There's not going to be any way to shut it off so will it be a near enough complete drain from whatever part that is? I can shut the header tank inlet in the attic, I guess that's about it.
 
Last edited:
That’s almost certainly a corroded pipe union or drain point on the backboiler, and if it’s dripping enough to soak floorboards, the metal is already severely weakened. Do NOT try to tighten it — old Baxi backboiler fittings often shear off when touched. And silicone won’t hold under system pressure; it’ll fail quickly.

Realistically, this needs a heating engineer ASAP, because a failing backboiler joint can escalate fast.
 
JeyHey said:
That’s almost certainly a corroded pipe union or drain point on the backboiler, and if it’s dripping enough to soak floorboards, the metal is already severely weakened. Do NOT try to tighten it — old Baxi backboiler fittings often shear off when touched.
Click to expand...

What complete and utter rubbish!
As has been said it's a spring loaded safety valve !
I'm old enough to have installed many.
No longer fit them, needs removing and a brass or iron plug in its place.
I'd just get some old towels and do it live.
 

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