Now that we have looked at the primary circuit, the heat sink radiator and pumped radiators we can look at the complete system in one circuit diagram. Firstly let’s look at a two port boiler stove:
Secondly let’s look at a four-port boiler stove (this is the easiest way of doing things in my opinion and no injector T required):
I have added two extras in this diagram, EITHER of which is demanded by Building Control in Document G (3.13). Of course you can fit both if you wish. The first option (B) is a valve that will close the circuit to the cylinder in the case of the cylinder overheating (set high at say 90 degrees centigrade) – a normally closed two port valve will do. The other option (that I choose) (F) is a temperature relief valve close to the top of the cylinder that sends water safely off to outside should the cylinder overheat (the same as somebody using a hot tap) NOTE THAT THIS VALVE NEEDS TO BE FITTED SO AIR CANNOT TRAP UNDERNEATH IT AND STOP IT WORKING – I.E. VENT NATURALLY AWAY FROM THE VALVE (essentially slide it into a pipe that is pointing uphill slightly away from the valve).
More in BOILER STOVES> Key Building Regulations.
Note: The pipe leaving the top of your coil (usually 22mm) should rise slightly between cylinder and where it meets the primary circuit so air is not trapped at the top of your coil. If you are looking for this on my diagrams above it is the pipe that “B” is strapped to. I also add a T off of this pipe with a manual 15mm gate valve on the end. Then, if air were to trap in the coil during filling (can happen) I can add a hose and flush it through.