Mains water expansion vessel on a combi system ?

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Hi guys - here's a quote from the 'Supply requirements' information for a combi boiler I'm interested in :

http://www.worcester-bosch.co.uk/index.php?fuseaction=product.detail&con_id=231281&detail_id=127860

"Where back-flow prevention devices, including water meters, are fitted the expansion of hot water into the cold water main can be prevented. This can result in a pressure build-up that may cause damage to the boiler and household devices such as showers, washing machines etc. In these cases we recommend that a mini-expansion vessel (Part No. 7 716 192 105) be fitted adjacent to the boiler in the cold water main."

Are expansion vessels fitted to the mains water inlet pipe as standard practice on combi systems, or aren't they generally necessary ?

I didn't have a separate expansion vessel fitted to the combi system in my last house, but then I didn't have a water meter.

I do have a water meter in my current house which is located in the pavement outside.

Will I need to get one of these expansion vessels fitted do you think ? Are there any other factors that I need to take into account ?

Cheers.
 
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I dont think most water meters have non return valves but in any case there is uaually plastic pipe on those installations which will absorm some expansion.

Only one or two manufacturers bother and the others dont seem to get any problems without them.

Tony
 
Why is the expansion vessel fitted on the cold mains when its supposed to be there for hot water that expands and needs somewhere to go? right?
 
I'm bringing this up again because we are seeing a number of combis that customers have had ongoing problems with, where the fitment of a water meter has caused significant overpressure situations.

In most cases this has not been diagnosed by the repairer, and in consequence leaks quickly reappear and the costs and breakdowns just keep coming.

A combi preheats the water and this expands. When all the taps are shut (ie: most of the time) this expansion is normally absorbed by the water main length.

A water meter effectively truncates the water main and it is down to your pipework to expand, which in many cases it is too short and rigid to accommodate.

The solution, which your boiler installer should automatically recommend, is a small expansion vessel needs to be fitted on the incoming water main.
 
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Note that what Simon is describing will only affect those boilers with built in preheat.

Tony
 
I'm bringing this up again because we are seeing a number of combis that customers have had ongoing problems with, where the fitment of a water meter has caused significant overpressure situations.

In most cases this has not been diagnosed by the repairer, and in consequence leaks quickly reappear and the costs and breakdowns just keep coming.

A combi preheats the water and this expands. When all the taps are shut (ie: most of the time) this expansion is normally absorbed by the water main length.

A water meter effectively truncates the water main and it is down to your pipework to expand, which in many cases it is too short and rigid to accommodate.

The solution, which your boiler installer should automatically recommend, is a small expansion vessel needs to be fitted on the incoming water main.


Could anyone advise whether the above is the case for a non- water metered house? I've been advised to get one from BG after they came to fix a leak on my Worcester.
Thanks
 
Yes some years ago my Main 7 heater did not switch off fast enough and it forced off a sweated joint, advised to fit a relief valve seems should have been fitted when boiler was fitted. Talking about 25 or more years ago, before the combi came in, had two independent boilers one for DHW other central heating, it was the DHW boiler that caused problem. It's nothing new, house built 1980 and non return valve fitted then.
 

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