Using ThermaTwin on an unvented (sealed) system

As ThermaTwin is designed to operate on an open vented system, it cannot be fitted onto a sealed or unvented system without additional intermediate components.

Replacing a recently installed or even new cylinder, just because it does not have a separate solar coil, makes no ecological or financial sense.

Help is at hand with the following simple retro-fit solutions.

We recommend the use of either:

a) A ThermaSyphon that isolates the ThermaTwin panel from the pressurised cylinder by using a separate chamber and

b) A ThermaPlug that replicates an electric immersion element heating the water instead of, or in addition to the back up electric immersion.

ThermaSyphon - an ideal solution for properties having an unvented system

The ThermaSyphon provides an ideal solution for properties that have a new or recently installed unvented system which does not have a separate solar coil. Changing a relatively new and well insulated unvented cylinder just to incorporate Solar Thermal makes no ecological or financial sense, so the ThermaSyphon is designed to stand alongside your cylinder with minimal additional plumbing.

Furthermore, in hard water areas, the ThermaSyphon prevents the build up of limescale deposits in the collector, which can potentially lead to premature failure of the panel. With the same water being passed again and again through the ThermaTwin unit, the water can be treated with a small dose of polyphosphate crystals, as the ThermaSyphon acts as the heat exchanger, providing fresh hot water into the cylinder.

ThermaSolar system

The ThermaPlug is a ‘plug & play’ insert into the existing cylinder, either replacing or complimenting the electric immersion heating element. Available in a range of sizes and fittings to suit virtually any cylinder, the ThermaPlug allows the ThermaTwin solar collector to constantly heat the water in the unvented cylinder without the collector becoming pressurised itself.

ThermaPlug is a ‘plug n play’ insert into the existing cylinder
Note: whilst the ThermaTwin collector is sized and designed to never boil, as an additional safety measure, there should be a heat dump on the supply to the panel to provide a failsafe in the event of the house being left unoccupied and the hot water unused during the summer months of highest solar gain.

ThermaPlug Installation


DiscreteHeat Company Limited
1 Victoria Works Industrial Estate
Coal Pit Lane, Atherton
Manchester, M46 0FY

01942 88 00 60
01942 66 51 04

VAT# 884427392
Company Reg# 5594330