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 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.
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 by-pass unless thermostatic radiator valves are fitted on every radiator
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”.
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
