Current guidance notes do not cover the connection of a solar thermal circuit to an unvented storage vessel (cylinder). However, if guidance is sought for compliance with current regulations the fundamental principle is to provide a failsafe means of shutting off the solar input to the heat exchanger if the cylinder temperature should rise above the set temperature of the cylinder's energy cut out. (See Note 1).
As with all unvented hot water systems, notification of intention to install should be given to your local building control.


Option A. A non self resetting mechanical shut-off should be installed on the solar primary flow to the cylinder. The mechanical shut-off should be suitable for use with a solar primary circuit (i.e. high temperature and glycol resistant). The mechanical shut-off should be integrated electrically with the cylinder energy cut out/s and if necessary the solar circuit temperature control, please refer to the solar controller manufacturer for further information.


Option B, Where the solar controller and hydraulic system demonstrate that by no lesser means the requirement in Option A is satisfied by other means; certification by an approvals body is required to demonstrate that in the event of the stored water going over temperature, the heat input to the cylinder is isolated by physical means and is non self resetting.
These systems should be clearly identified with reference to the approvals body. (See Note 2)


Note 1 : Whilst most solar cylinders use a coil type heat exchanger other options such as external plate to plate devices , external annulars or ‘tank in tank' systems may be used but the same control options always apply.

Note 2 : Current approved bodies include the British Board of Agrement (BBA) , WRc-NSF Limited, or KIWA