Question from Alan Hyatt, via email:
I have a question surrounding the connection of a non-thermostatically controlled heat source to an unvented indirect cylinder.
Would control of the Domestic Hot Water temperature via an immersed or clamp on stat and motor open spring close valve – V4043H – (with the end switch turning off a circulator and disconnecting the supply to a motor closed spring open valve – V4043B – which in turn is in the circuit to a 3kW heat dump radiator) be considered sufficient control, so as not to contravene the Building Regulations? i.e. The system fails safe even in the event of a power failure when a log burning/solid fuel stove is in use.
Also what is the difference between the above and the uncontrolled heat of the sun (solar thermal systems)? At least the solid fuel appliance can go out.
Response from Martyn Bridges, director of marketing and technical support at Worcester, Bosch Group:
The basic requirement of G3 of the Building Regulations states:
(3) A hot water system that has a hot water storage vessel shall incorporate precautions to:
(A): Prevent the temperature of the water stored in the vessel at any time exceeding 100ºC
(B): Ensure that any discharge from safety devices is safely conveyed to where it is visible but will not cause a danger to persons in or about the building.
Under the G3 guidance under the section performance, it states:
In the secretary of state’s view requirements G3(3) will be met for a hot water storage system that has as (an) unvented storage vessel if the storage vessel has at least two independent safety devices such as those that release pressure and so prevent the temperature of the stored water at any time exceeding 100ºC in addition to any thermostat.
It goes on to state further requirements, however, I believe your suggestion would contravene the regulations, as you are relying on a thermostat to engage or energise the safety circuit to the heat dump. There would also be the concern that in time the heat dump could be up to temperature and there is no place for the heat to disperse to.