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6.3 Primary & Renewable Circuits
The working pressure and temperature for all heat exchanger coils is given in Table 1. All
connections to the cylinder must be made using compression fittings.
Ensure that the correct concentration and type of corrosion inhibitor is used for the system circuits
heating the coils / heat exchanger. This must be checked concentrations adjusted as required
during annual service.
Safety thermostat
Each heat exchanger coil has an associated combined control & safety thermostat. The system
controls must be wired in such a manner as to cut off the flow of heat to the cylinder in the event
of overheating in order to comply with Building Regulations and to ensure a safe installation. This
is typically achieved using a motorised valve wired in series with the thermostat. Refer to Section
6.11 for suggested wiring schematics.
Motorised valve
A motorised valve is supplied with Indirect and Twin Coil models. This must be fitted to the
pipework supplying the primary coil (usually the coil connected to the heat source) and wired in
series with the combined control & safety thermostat in order to comply with Building Regulations
and to ensure a safe installation. In this manner, if the heat source malfunctions and produces
excess heat, the motorised valve will close preventing the cylinder from overheating. Refer to
Section 6.11 for suggested wiring schematics.
Uncontrolled solid fuel boilers and gravity circulation systems must not be used with an
unvented hot water system. For guidance on connecting a controllable solid fuel appliance (such
as a wood pellet stove or boiler) to an unvented cylinder, reference should be made to the
appliance manufacturer’s instructions and to Building Control.
Solar installations
If connecting a solar thermal installation, for example, to the renewable coil of a Twin Coil cylinder,
the controls must be wired in series with the combined control & safety thermostat.
Refer to the solar
appliance manufacturer’s instructions and to Building Control for further
guidance.
Heat Pump Cylinder installations
Heat Pump cylinders can be used with a circulating pump designed for potable water installations
in conjunction with a plate heat exchanger.
The power supply to the circulating pump is to be controlled by the thermostat fitted to the cylinder,
refer to section 6.11.5 for details.
