>> I wouldn't want to sleep next to the blinkin' thing
I've been covering boilers and hot water storage at college over the last couple of weeks - let's see if I can remember it all...
BS EN 60335-2-73 ensures that boiler explosions cannot happen in newly installed systems, as pmh says they are fitted with a blow off valve as a last resort. The hot water storage cylinder and the pipework are designed in such a way that the conditions for explosion can never arise - explosions are caused by pressurised superheated water (>100°C) being subject to a sudden drop in pressure such that a state change occurs and the water expands 1,600x in volume as it turns to steam. Wholesome hot water should be kept at no more than 82°C by thermostatic control, and all of the components in a high pressure unvented system are designed to fail safe.
In answer to the OP's question, rtj70 has the right idea about doing a comparison test over 2x 7-day periods and balancing energy consumption with system performance. The installer is unlikely to be on a kickback from your energy supplier, therefore the advice to run it 24 hours a day is likely to be aimed at getting the best performance from your hot water supply.
And to Everest Pete, stainless steel is used rather than copper because domestic water (especially soft water) is slightly acidic and can corrode copper cylinders and pipework. Bacterial growth only occurs in systems with a cold water storage cistern in the loft - it can be prevented by keeping all light out out of the cistern. This is achieved by fitting a Byelaw 30 kit consisting of an opaque, well fitting cover over the cold water cistern with mesh screens on the ventilation and overflow pipes. The OP's high pressure unvented system does not need a loft cistern.
Hth,
Dave
Last edited by: Dave_TD {P} on Sun 23 May 10 at 23:30
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