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Adrian Games · Sep 6, 2019

Hello all, just found a small drip on a pipe from our open fire back boiler. There is a oil fired utility boiler and an immersion heater. There are 4 pipes coming from the back boiler and the photo show one of these with a fitting which looks like it came out of the ark. Can any one tell me what it should do and suggest a modern replacement. ( please see attached photo). many thanks, Adrian

Harvest Fields · Sep 6, 2019

A man walking his dog?

Darren Jackson · Sep 6, 2019

Looks like an old air vent to bleed the air out of the system, you could either replace the washer or replace the air vent with - Air vent cap

Stigster · Sep 6, 2019

Darren Jackson said:
Looks like an old air vent to bleed the air out of the system, you could either replace the washer or replace the air vent with - Air vent cap

Either that or an ancient pressure relief valve. If so there will be (or would have been!) a spring loaded doodad in there to keep it closed unless there is an overpressure situation. I believe the screw threaded top end was there to adjust the tension and therefore the pressure at which it will discharge.

Millsy 82 · Sep 6, 2019

Another vote for a pressure relief valve.

firemant · Sep 6, 2019

Yep, PRV. On gas boilers we routinely replaced leaking ones with a plug, as they were not neccessary.

snowhead · Sep 6, 2019

I think it looks a lot better this way up;

I'd vote for Pressure relief if the screw in the top is locked with a nut.
A direct replacement is probably going to be hard to find, it may need a slight addition to the pipework to get a modern one in

firemant · Sep 6, 2019

snowhead said:
I think it looks a lot better this way up;

View attachment 40279

I'd vote for Pressure relief if the screw in the top is locked with a nut.
A direct replacement is probably going to be hard to find, it may need a slight addition to the pipework to get a modern one in

Are they even still available? I haven't looked, but I would expect any modern PRV to be expected to terminate outside. I do not do Oil, but gas boilers that had these fitted also had an Vent pipe and a Cold Feed, both of which render a PRV redundant - so they would never be replaced. Is this not the case for Oil (serious question)

ShaunCorbs · Sep 6, 2019

Yes still available bes have stock

But depending on the system change for an manual air vent or prv

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Adrian Games · Sep 9, 2019

Many thanks to everybody who replied, I have a little more data, if it helps. In the roof space are 2 water tanks, a small one which supplies the rads, boiler and heating coil in the immersion tank. This tank has 2 vents returning to tank, the other tank is larger and supplies the immersion tank with water to heat for the taps, this tank has only one vent. when using the open fire with the back boiler on draw, the water will boil in the back boiler after a couple of hours and the steam can be heard venting in to the tank, So I wonder whether the valve is letting hot water/steam back to the tank, or if the valve activated, would steam come out of the ring of holes? Would it need a pressure valve if open vented to the tank? Really not looking forward to touching anything without a plan. When using the back boiler, it heats the water cylinder by convection current.

Stigster · Sep 10, 2019

It won't be allowing steam/water to go up the vent, that will be an open path and should have no devices or valves impeding that at all. Water in such a system usually has two places to expand, up the open vent and also back up the cold feed to the header tank. The pressure relief valve (the consensus seems to be that's what it is) will be there for the unlikely but potentially catastrophic event that those two expansion pathways are blocked or otherwise closed off. People have been known to do crazy things like not understand why the vent is discharging steam or water and capped the vent off. If they do that there is only one path for expansion - the cold feed. If someone then closes the valve on the cold feed you've got yourself a bomb.

That's where the spring-loaded Pressure Relief valve comes in. It a belt and braces kind of deal.

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