Mini Expansion Vessel?

As per posts above - they want a mini EV, to take up any expansion / water hammer effects on the cold mains/DHW circuit, likely due to customer being on water meter.

Water meter installs usually (always?) include a check valve in the circuit - therefore WB dont want high static pressure caused by suddenly closing the tap to blast out a seal from the plastic waterblock.

From Greenstar CDI manual
Where the mains water supply has a non-return, back flow prevention valve fitted, a mini expansion vessel must be connected to the mains water inlet pipe between the non-return valve and the boiler.

Click to expand...

guess it is mandatory then.

twas fun thou

it's only really new boilers that may need them to stop the boiler leaking as they just aren't made like they used to be! it's not really to prevent water hammer but just to cover up the fact that the boilers leak too easily!

Just for the record:
I bought a house in the country, with a Worcester kerosene (Paraffin-oil) boiler about 10 years old.
I did the calculation that I had more bedrooms than people and decided that a water meter was a sensible option.
Nobody told me that water meters incorporate a non return valve.
So when I turned on the boiler for the winter its "slave-tank" of hot water [Paraffin does not have enough heat to work like a natural gas combi] duly expanded and the rising water pressure had a choice of squashing the diaphram in the mini expansion tank or trying to back-up into the rising main.
Well the mini expansion/knock preventer thing the size of a swan's-egg-cup, had not been re-pressurised in the 10 years, as the previous owner had no idea of how his boiler worked.
The mixing valve in the boiler (which gives priority to the hot water) burst its gasket - fortunately the boiler is outside of the main house - and it was my wallet that took something of a knock.

I was reading up on this recently as part of my mains hot water via plate heat exchanger plan- with any closed heating or hot water system there is the possibility of expansion of heated water causing excessive pressure in the pipework. Back in the day that excess pressure would be sent back down the water main, nowadays with backcheck valves it needs to be catered for in house. Only needs a tiny vessel cos overall dhw pipework volume will be v small- 20, maybe 30 litres in a big house- cost me £15 i think for a 2 litre vessel.

I have just taken out a WB Maintenance contract on my 12 year old boiler, as it is starting to get old. They asked no questions.

As for the water meter, I was just given one a few years back, no checks no nothing.

I posted this thread 11 years ago lol.
Might be better to start your own if you need support rather than bumping a 11 year old thread? lol

Do u still have your hair?