No hot water

1 May 2005
Reaction score
United Kingdom
I've just had an unvented hot water cylinder installed in my bungalow. The boiler is an oil fired worcester bosch danesmoor 20/25 it is an open vented system. The original indirect cylinder was situated next to the boiler about 6" above it. The system top-up tank is in the attic. There is no 3 way motorised valve only a circulation pump. The unvented cylinder has been installed in the attic & the system fill tank lifted to 1.3 metres above the flow/return pipework for the cylinder. Any suggestions as to why there is no hot water. The flow/return pipes to the cylinder only get warm about 2-3 feet above the boiler. Any help appreciated. :confused:
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It sounds like an airlock in your primary F&R to the cylinder. - are you getting heat to the rads?

Also, the unvented cylinder will have been supplied with a 2 port Motorised zone valve (a legal requirement if the unit is approved) - make sure this is fitted and controlled properly to ensure it is opening to allow the boiler to heat the cylinder.

You say 'I've just installed' - are you a registered unvented installer?(or did you mean 'ive just had installed'?) - whichever, not fitting the 2port MZV contravenes current UK building regs

Hope this helps
Thanks coppercylinderman. I've had it installed the central heating is fine and I can't see a valve anywhere in the f/r pipes to the cylinder. Where should it go and what operates it.
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I used it to replace unprintable comments. Dangerous and incompetent would nearly cover it. If you chose to you could get the installer prosecuted. Quite heavy fines per day of that violation of building regs.

If your house blows off the face of the earth tonight, you'll know why. If it's been installed all wrong, the only way you can be assured of safety is to turn the water mains, and the heating, and any electric immersion heater, off.

There's a famous photo of half a 3 storey French school. The other half got spread over the countryside. At 6am, luckily.

You are looking for a motorised zone valve (the make depends on who's cylinder you have had installed) on the flow to the primary coil in the cylinder.

There is no ambiguity in the regs - you either fit it, or you have not got a legal installation.

Every manufacturer will supply one.

As Chris said, the penalties can be severe if you take it far enough - your own liability will be that if anything does happen (unlikely but not impossible) your buildings & contents insurance is probably null & void.

Bottom Line - GET THIS SORTED!!

Hope this helps.
Has the local authority been informed of its installation :?: and has the benchmark book been filled in. :?:
It is a legal requirement that this is done.
The installer must be qualified to work on unvented to be able to self certify the work.
None existence of 2 port Motorised zone valve implies that the installer has not done a proper job
NO 2 port valve also means NO thermal overheat cut-off, as the guys are saying the system is dangerous, and needs to be sorted quick.
Thanks to all. I will contact the authorities as I can't get a reply from the tosser who installed it.:cool:
I dont want to sound like a pedant, but slugbaby isnt completely right, and if Bilbo is taking it further, he should get it spot on.

The benchmark book isnt a legal requirement - some manufacturers provide one to keep a servicing record for the guarentee, but not every unvented cylinder has one.

The legal requiment is that the installer MUST complete the badge on the cylinder. The cylinder badge contains information required by the building regs.

Good Luck Bilbo

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