unvented hot water system blow off valves.

[mark]

I am aware that unvented mains pressure systems need to be installed by an approved plumber and need some form of pressure relief valves installed.

I assume ch boilers have a valve included on the heating side but another needs to be installed on the mains fed side.

But how many? When do they get tested? How are they tested? Do they get tested? Should they be renewed? When should they be renewed? Are they adjustable? Should they be adjustable?

Cheers.

[Aidan]

Unvented hot water storage systems, with a capacity of more than 15 litres.

Are you referring to unvented hot water storage systems or combi boilers?

For unvented hot water storage systems, the answers are;

2, they come with the kit, pressure relief and T&P relief valves.

Checked during ammual service to see they can open, not tested for pressure or temperature settings.

Twist the knob to see that they open & reseal.

Should do.

If they don't work or if they drip.

When they stop working or start dripping.

No, factory pre-set..

No.

[Ed Sirett]

...two or three valves quite specifically chosen.

From you post it's probably that you are not familiar with how things are laid out. Either or both of the heating system and HW cylinder may be unvented. The main FAQ and the SealedCH FAQ see below are starters.

There is no water connection between the heating circuit and the HW cylinder.

2 or 3 on the cylinder.

Ideally cylinder ones should be tested annually. Boiler ones should be left alone, they are tested on installation.

By lifting the test levers or rotating the test knob.

Not usually. Except people fiddle with the boiler one in desperation when things go wrong.

Only if they dribble prior to their set pressure or temperature.

As above.

Over my dead body.

As above.