Unvented hot water system - increase the pressure?


Postby sanderr2 » Thu Dec 09, 2010 1:43 pm

Hi, I've recently moved in to a property with an unvented heating system (with an MHS Strata 1 boiler). The two showers on the middle floor don't have a great throughput - I installed a pump in our old house (which had a vented heating system) which delivered a fantastic showering experience.

In my research it appears that I can't install even a single pump to boost the hot water pressure to one of the showers so I would be very grateful if anyone could provide advice on any options I have for getting decent water pressure at the showerheads.

The boiler is in the cellar with a separate pressure tank. The hot water tank is on the same floor (1st) as the showers. I noticed that there is also some form of pressure vessel off the hot water tank - it has a label stating that this needed re-charging every 6 months but it's an Italian product and the manufacturers website gave no clue how to do this - I was thinking that maybe the pressure needs increasing here?

I had to re-pressurise the boiler a couple of weeks ago and MHS stated that it shouldn't be running at more than 1.1 bar - does this have any bearing on the pressure achievable at the shower head or is it just a red herring?

Thanks in anticipation,
Rob
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Postby stagbeetle » Fri Dec 10, 2010 12:24 pm

Rob,
I too have a house with an unvented system. The hot water tank is pressurised by the cold supply. So the hot water should be available at the same pressure as the cold supply.
However, I can't open the shower valve fully because the drain is unable to keep up with the volume of water and I run out of hot water too quickly.
Is your cold water pressure low?
If it is then a pump could be used, but not directly off the mains. You would need the main supply to feed a header tank which would then feed a pump which would feed the hot water storage tank with water at a greater pressure.
However, I believe that the water companies are obliged to supply water at a sufficient pressure. So it may be worth speaking to them if your mains water pressure is low. There could be a problem with the size of the supply pipe causing restrictions or a faulty tap where the supply joins your property.

I don't think that the boiler pressure or air pressure in the vessel(s) have any thing to do with little water at your shower head.

It is also worth mentioning that some shower valves are very restrictive and designed to be used with high pressure pumped systems. If you get a decent amount of water out of your bath hot tap this would that there are restrictions to the shower heads.

Regards.
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