Unvented hot water system - Pressure problem

24 Feb 2016
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United Kingdom
Hi all

We have an unvented hot water cylinder. I understand that the hot water pressure should be the same as the cold water pressure.

Unfortunately, we have really good cold water pressure from all taps and showers, however the hot water pressure is much lower.

Could there be a simple reason for this please?

Thank you for your help.

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Between the incoming cold water and your unvented cylinder there is a device, part of the purpose of which is to regulate the pressure of the cold water going into the hot water cylinder. This device normally has a second outlet, which is generally used to supply all the cold taps / outlets in the property, thus ensuring hot and cold are the same pressure. If however the cold supplies are taken off before the pressure regulator, then they may be at a higher pressure than the hot water.

For anyone to work on an unvented cylinder or its controls they must have a "G3" qualification, and you might wish to get someone with this qualification to inspect and give you a definitive answer.
Thank you, that is helpful.

Is there a way of upgrading the device to allow the hot water cylinder to provide hot water at a higher pressure please?
No, its the other way round! The cold pressure needs to be the same as the hot so lower pressure.

Of course if you have not bothered to get the cylinder serviced then the hot water filter may be blocked. That would be indicated by a higher static and low flow pressure which reduces as more flow is taken.

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Thank you. That's interesting.

How would I recognise a "higher static and low flow pressure which reduces as more flow is taken" please? When we turn on a hot tap or shower, there is a moment (less than a second) of really high pressure which then drops to the lower pressure. Could this indicate a blocked filter?

It is a new (to us) house so we have not yet had the cylinder serviced, but we will do now! Thank you.
Make sure the service includes cleaning the filter.

To check the pressure you need a pressure gauge!!!


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