Fully Pumped Systems (also see the picture gallery and System Basics) The term for any boiler that uses a pump to move all the heat from the boiler to every part of the system is fully pumped. As a rule one pump is used to circulate the water through valves which divert the flow to the relevant part of the system. With fully pumped systems you have a lot of control over what gets warm, at what time and to what temperature you desire, providing to correct controls are fitted. With all fully pumped systems that stores hot water in a cylinder then you can have an electric Immersion heater as a backup for the hot water in case of a failure of the gas CH system Central heating is only as good as the controls that are fitted. The next few systems show types of controls and have a wiring diagram containing a simple sketch in the bottom LH corner. The sketch shows the basic pipe work from the boiler to the valve/s and cylinder. "Y Plan" (3 Port Mid Position) probably the most popular system in existence. Y plan Photograph Y Plan Wiring Diagram The Clock (Programmer) is set to come on at the desired times. At the time for coming on the clock sends a signal to either the room thermostat and/or the cylinder thermostat. If one or both require heat then a signal is sent to the Y plan valve. The valve then swings into the correct position for the demand e.g. if the room stat is calling for heat, then the valve diverts and all the heat from the boiler is sent to the radiators. If the cylinder stat calls for heat then it is sent to the cylinder. But if both are calling for heat the valve goes into mid position and lets everything warm up together. The valve itself turns the boiler on if there is a call for heat, and off again when there is no call for heat. (satisfied) Very economical to run, dependent on which type of boiler is fitted, but should not be used with a combination boiler. Possible problems No heating but Hw OK- this is usually the motor that needs replacing within the Motorised valve
No heat or Hw- probably the pump needs replacing System sluggish & expansion tank getting hot- Cold feed blocked and possibly not piped up correctly, to check for a blockage use a magnet and touch it to the copper pipes, if the is an attraction then there is sludge inside the pipes, this is caused by either not being flushed out properly when new or the cold feed and expansion pipes are not configured correctly, this also causes radiators to leak but will take a few years to corrode through completely "Home Warm" Almost the same system as a Y Plan (Not recommended) Home Warm Wiring Diagram This system was a low cost version of the Y Plan, except a Primatic cylinder is used and the pump is on the return. (Using a Primatic cylinder is not recommended on a fully pumped system) "S Plan" Probably the most versatile system. S Plan photograph S Plan Wiring Diagram With this system you can have as many zones as you like, but each zone must have its own valve and thermostat. A popular way is to have 4 valves, 1 for the hot water, 1 for upstairs,1 for downstairs and 1 for say, the conservatory. When the clock calls for heat at the required time it sends a signal to one or more of the thermostats. If in turn the thermostat is calling for heat, then power is sent to the zone valve it controls and drives the motor open. When it is fully open a micro switch is made, which turns on the boiler and pump. Once the thermostat reaches temperature the power is turned off to the zone valve which springs shut. The micro switch brakes and so power is cut off to the boiler. (providing another zone is not open) Note, if there is a Pump over run on the boiler then a by-pass must be fitted.
Very economical to run dependent on which boiler is fitted (ideal for use with any type of boiler, even a combination boiler) Possible problems No heating but Hw OK- this is usually the motor that needs replacing within the Heating Motorised valve No Hw but heating OK- this is usually the motor that needs replacing within the HW Motorised valve No heat or Hw- probably the pump needs replacing System sluggish & expansion tank getting hot- Cold feed blocked and possibly not piped up correctly, to check for a blockage use a magnet and touch it to the copper pipes, if the is an attraction then there is sludge inside the pipes, this is caused by either not being flushed out properly when new or the cold feed and expansion pipes are not configured correctly, this also causes radiators to leak but will take a few years to corrode through completely "G Plan" This is another system like the S Plan except the valves are normally open. (V4043) G Plan Wiring Diagram When the clock switches on it sends power to the thermostats, if a thermostat calls for heat the power is sent directly to the boiler and pump. Once a thermostat is satisfied it switches power to the zone valve and a motor drives it shut. When all zones are up to temperature the power is cut to the boiler. When there is another call for heat, the thermostat switches power from the zone valve (which springs open) back to the boiler. This system doesn't need a bypass unless thermostatic radiator valves are fitted on every radiator "SMC Controller" This is an old type system but all the parts are still available but a twin pump system like this has just been re-launched
SMC Wiring Diagram When there is a call for hot water, the hot water pump runs and turns the boiler on. If there is a call for heating, the central heating pump runs and an electrical relay turns the boiler on. Although this system has proved reliable some of the replacement items are quite expensive. If you are changing your boiler then I would advise you to update to a different system A "Y Plan" would be an easy replacement "W Plan" (Diverter Valve) W Plan Wiring Diagram Again, this is an older system, at first glance this looks like a Y Plan except the valve is a diverter valve which means two position so it can only do one circuit at a time. When the clock comes on power is sent to both cylinder and room thermostats, if the cylinder thermostat is calling for heat, the power is sent to the boiler and pump and the Motorised valve stays at rest. This lets all the heat from the boiler flow to the cylinder, even though the room thermostat might be calling for heat, this has no effect. Once the cylinder stat is satisfied power is switched to the valve, closing the water circuit and opening the heating circuit. If the room thermostat is calling for heat, then power is sent to the pump and boiler pushing the flow through the now open heating circuit. This will continue until either the room thermostat is satisfied, in which case the boiler and pump will shut off, or until the cylinder thermostat calls for more heat. The boiler and pump stay on, but the valve springs back into the hot water position. This is known as hot water priority. Whenever you come across this valve it is advisable to change it to a Y Plan valve ( some wiring to alter)
W PLAN With Priority Switch Priority Wiring Diagram Same as W Plan (above) except a more complicated clock is fitted allowing choice of either hot water priority or heating priority. So in the case of heating priority the hot water will remain cold until the heating has been satisfied If you are converting an existing Gravity Hw system to fully pumped then the new boiler is best located near the cylinder or even in the cylinder cupboard as the Motorised valve is best situated next to the cylinder then the existing gravity circulation pipes which go down to the old boiler location can be reused to connect up the heating system to the Motorised valve, also the domestic HW return is automatically in the correct place