Explain this boiler system...

[Multiplex]

Hi there,

We're moving into a new house and it has this brand new boiler system that I don't understand at all.

Can someone explain what the small red and white cylinders are for?

Does it look like a good system?

I hate having something that I don't know how it works. I've seen some diagrams on the internet but it's very difficult putting it all together.

Thanks,

Simon.

 

[ChrisR]

Those are expansion vessels/pressure vessels. You have an unvented hot water storage system. That's why your hot water is mains pressure. When the water expends on heating it goes into the white vessel. The heating for the property is also sealed - that uses the red one. You will have a pressure guage for the heating system which should be reading about 1 bar, and afilling loop, usually siver braided , which you use to top up the pressure. (tap(s) at the ends of the loop may need a screwdriver to operate them). It will drop slowly but should be OK for several months.

It looks neat enough but the primary pipes from the boiler to the cylinder should be insulated- you're trying to heat your water with those, not the flat. One is the pipe with the "stalk" sticking up and the return is the one parallel below it.

Your UVHWSS needs annual maintenance, get it done at the same time as your boiler. You know, like everyone does...

 

[brumylad]

maintenance is a good idea, the unvented hot water systems presumably have a good safety record, they have been in use in the US for years. They have only recently been permitted by building regs to be installed in the uk.

The fear is that if the 3 safety devices fitted to the unvented cylinder fail, the water inside becomes super heated and under very high pressure. When the cylinder finally splits under the increasing pressure, the super heated water will undergo a flash change to steam. This event would be a large explosion that would destroy the property and I guess the occupants too.

Make sure your chosen service engineer is CORGI registered and has experience of unvented hot water cylinders. They are still quite rare.

 

[ChrisR]

Regarding brum's last paragraph, note that Corginess is nowt to do with competence on uvhwss, which resuires a separate qualification, for which an i.d. card is issued. I think mine has "HOT WATER" or something equally enigmatic, across the top.