Spring Safety Valve - do I need it?

Sounds more like an air bottle. This is an automatic bleed valve, rather than a safety type. They've usually got a manual valve to seal them completely after they've initially vented the air out of the system. After that, they shouldn't be required.

I was picturing the old pressure relief valve on my parent's heating system, which dates back to when they used to have a solid fuel boiler. Similar in principle to the ones used nowadays on sealed systems, but with no knob and just a set of holes round the top which let the steam out into the room.

That was my original thought, but it looks more like this:

Still not sure what to do - I suspect it will probably be okay without unless anybody else replies with a viable explanation of why I should put one in.

I've never seen one on a vented system. Have you got a copy of the installation instructions for your boiler? Unless they explicitly say that you must have one of these valves, I would forget it.

If you have removed the safety blow-off valve and plugged it up, DO NOT USE your boiler at all. Switch it off NOW.

Would be nice if you would back that comment up with some reasons why you beleive the setup to be dangerous.

A new one would probably cost you about =A35; why would you omit it?

It isn't necessary, assuming that the open vent pipe doesn't freeze, get blocked with limescale, valved off by a fool, and that the boiler is installed correctly in the first place and that it isn't later altered to a sealed system.

It is good practice to fit one on a boiler. I can recall a technical note from my employers, an education authority, some 20 years ago specifying pressure relief valves on all hot water storage vessels and boilers, even if they were vented.

I've never seen a vented system without one.

Most if not all certainly used to say you need one in case of any system malfunction which blocked the overflow. As it is already there and the cost of replacing it is trivial it scarcely seems worth not having it compared with the slight but potentially serious risk of not fitting one.

AFAICT they seem to be included on vented systems when the pipework does not have a continuously rising vent pipe. This tends to occur on systems installed in flats.

What Drivel finds dangerous is quite random. In another thread he may well advocate a dangerous practice whilst in yet another suggest doing a pile of unnecessary extra work.

In this case I'd be guided by the installation instructions. Adjustable relief valves are available in the BES catalogue.

They were taken away, in favour of superior boiler controls, as if they blew off they could in someone's face.

What dangerous practices are you talking about? cite please.

You have just advised me to replace something which you think may "blow off" in my face.

I've just done the one on my Potterton which was leaking. Very simple job though as after removing the cap and spring it turned out that the brass plunger behind them just took a standard 5/8" tap washer. Maybe yours has some sort of replaceable washer inside too. If your boiler has a permanently open vent somewhere else that steam can escape from then the safety valve should be redundant. My system did have another vent into a loft tank but it kept overflowing and steaming the loft up so I capped it off a few years ago.

-- Dave Baker

If it is in a position there it can blow into someone face. cap it up and relocate, but it must be near the boiler. Sometimes it is best inside the case.

The blow-off valve is a last resort in case the open vent is blocked.