Leaving feed to header tank closed

In an unpressurised system with a feed tank in the loft, is it safe to turn off the supply of cold water to the feed tank once the system is filled & bled?

I've got a niggling anxiety that if a joint or fitting goes, the feed tank will keep being supplied from the mains and could flood the house, in comparison to a pressurised system which has a fill loop that's normally left closed.

Only risk I can think of is that if there is a minor, hidden leak and the system gradually empties it could lead to dry running, but I think I'd notice the upstairs radiators getting cold.

Yes, you should notice issues with water loss before anything gets too serious. However the Central Heating shouldn't be at any greater risk than any of the other Plumbing in the property.

1. The Feed and Expansion (F&E) tank should have a float valve to turn the water off once the correct level has been reached.
2. In addition, the F&E should have an overflow running to outside to run any excess water off in the event of float valve failure. Wouldn't hurt to test the overflow isn't blocked and can cope with a full flow overflow. This should stop any flood occurring.
3. If not replenished from the mains, the F&E will eventually run dry through evaporation, although this could take months.

oldbuffer said:

1. The Feed and Expansion (F&E) tank should have a float valve to turn the water off once the correct level has been reached.
2. In addition, the F&E should have an overflow running to outside to run any excess water off in the event of float valve failure. Wouldn't hurt to test the overflow isn't blocked and can cope with a full flow overflow. This should stop any flood occurring.
3. If not replenished from the mains, the F&E will eventually run dry through evaporation, although this could take months.

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You've misunderstood my concern - if a push fit joint in the central heating plumbing pops apart the feed tank will empty, the float valve will open and the mains water will top it back up, meaning that faulty joint will keep leaking forever and flood the house. If I turn off the supply to the feed tank and this happens, at worst the existing contents of the CH system will empty through that joint, but then it will stop.