Santon PremierPlus Unvented System

22 Feb 2009
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United Kingdom
I Have just had a Santon Premier Plus unvented systems installed. We have a problem in that the water runs hot out of taps but some showers (where the flow is restricted due to shower head)start hot but quickly turn stone cold. My plumber thought it was cold leaking into the hot system through a mixer tap but I'm fairly sure it's the tank. Plus the pipe at the top of the tank turns cold when running the shower but warms up when the hot tap runs. Hope you can help! :(
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assuming that all the hot water comes from the same outlet

the problem i suspect is that the cold pressure is greater than the hot which passes through a pressure reducing valve on the way into the cylinder
the cure is to put a pressure equalising valve in the supply pipes to the shower
I think that Kevin has correctly guessed whats happening!

The correct solution is to feed the shower and any mixer type taps without non return valves fitted directly from the pressure reducing valve on the cylinder.

Unfortunately many installers dont bother to do that or even discuss it with the customer.

Did your installer have the G3 qualification and complete the Benchmark certificate?

Yes would agree, certainly sounds as if you have unbalanced H&C supplies and should be fitted as Tony describes.
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if you have the space in the pipework below the shower an equalising valve would be the quickest / cheaper option than running a new supply but seldom do builders/plumbers allow enough space to put it in
the valve is about 5" cube
Thanks Kevin, Tony and Dave.

The plumber is due back tomorrow. I'm not sure if the equalising valve could be fitted due to space. Plus I have 3 showers!!

Tony can your solution be applied to the pipework coming from the tank where we have access. i.e. is it an alternative to the equalising valve? Basically I need to explain the problem to the plumber (plus ask about the G3 qualification and Bench Certificate (are they needed by planning officers?)). I can then offer a solution (possibly) without the need to start removing tiles etc :(

you could put a pressure reducing valve on the incoming mains
in this case then tony is right. previous expierience of this won't cure this problem as it is difficult to get the two to the same pressure
in this case the cold will need to go through the same reducer as the supply to the cylinder to be effective
couldnt you just take the shower cold feed from after the unvented prv?
Its not the correct solution but a 15 mm reducing valve on the cold feed to the shower will often solve the problem if its set a little below the pressure of the hot cylinder.

The only way to get optimal performance is with balanced feeds to the shower with the same reducing valve supplying both. Anything else will have different dynamic characteristics.


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