Question from Malcolm Judd, via e-mail:
Keeping water hot at 70ºC to combat legionella means using blending valves to bring water to a safe usable temperature. With cistern style water heaters, we need blenders that work at less than one metre head with higher cold pressures. Do you know of any?
Answer from Martyn Bridges, director of marketing and technical support at Worcester, Bosch Group:
Cistern or cold water cistern (or tank) fed storage systems operate at a significantly lower pressure than mains pressure cylinders. I have looked through a number of TMV manufacturers information and all of these valves appeared to operate at a minimum of 0.2 bar and not the 0.1 bar you request.
My suggestion would be to install the TMV’s at the point of use, which is hopefully lower than the cylinder where you may achieve the 0.2 bar requested. Unfortunately, this may mean that you have to install more than one TMV, therefore if you have sufficient height it may be more cost effective to raise the cold water storage cistern until two metres of head (0.2 bar) is achieved.