Filling central heating on unvented cylinder.

8 May 2009
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United Kingdom
Just been to refill an unvented system in a house that was drained down last october. It was fitted with an unvented cylinder, although the ch was gravity fed from the loft. Filled ch and bled rads. No vent pipe into ch feed tank. When I turned on the boiler (standard open vent Potterton) it overheated and locked out after about a minute. Checked pump which wasn't running.

1, Would the seized pump be enough to lock out boiler? There wasn't any banging or noise.

2, There are no vent points in airing cupboard for the ch. Is the expansion vessel fitted to the unvented tank there for ch expansion as well as hw?

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Sounds like you have a combined feed and expansion se up.

These can often be slow and problematic to fill and get air out of, but sort out pump first.
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