Answers please!
I have been advised to fit a differential bypass valve to a Gravity fed CH system with rads controlled by TRV's. I understand what the valve does, but is it neccessary and where to locate it? Thanks JC.
It is necessary if you either have S-Plan plus, or insufficient un-TRVed radiator capacity. However, it is not appropriate as the only bypass on a system that has a boiler not suited to sealed pressurised operation. Such a system must have a manual bypass valve, as it relies for safety on a supply of low pressure quenching water that will not operate an auto bypass valve which requires considerable pressure to open.
Stick in anywhere on the unzoned pipework after the pump, unless the boiler manufacturer specifies a minimum loop size, which might dictate position.
Christian.
I didn't mean S-Plan plus, but any S-Plan or derivative...
Christian.
I'm not quite sure what you mean by gravity fed. If you mean that the HW is heated by means of an unpumped gravity (convection) circulation system, with the CH being pumped, then you're very unlikely to need a by-pass valve.
If, on the other hand, it is fully pumped - and by 'gravity fed' you mean it's a vented (unpressuriesed) system, it may or may not need a by-pass. It depends, to some extent, on whether the pump is controlled by the boiler in order to provide pump over-run - i.e. to keep the pump running for a while after the boiler stops firing, to carry away the residual heat. In this case, the water must have somewhere to go during the over-run period. If you have an S-Plan system whose zone valves can all be closed - or any system where all the rads have TRVs fitted - you will need a by-pass if pump over-run is required.
The inlet of the by-pass needs to be connected to the flow pipe, after the pump but before any zone valves. The outlet needs to be connected into the common HW/CH return.
Cristian, Roger, your answers were just what I needed.
Thanks, JC
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