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What IS a SysteMate III?

The SysteMate is a close relative of the BoilerMate. They are both thermal stores heated by a separate gas (or oil) boiler, and they provide almost instant heat to radiators when the heating is turned ON, and large quantities of mains-pressure hot water to hot taps and showers.

The difference between the two is that the boilermate has an open-vented store, topped up by a header tank, and therefore cannot be connected to any radiator higher in the building than the height of the header tank. The SysteMate has a pressurised, sealed system radiator circuit, so can have radiators installed above the appliance. 

The SysteMate III is circular in footprint with pumps, valves, heat exchanger all attached rather untidily to the outside. The SysteMate 2000 on the other hand has a square outer case and all the gubbins (technical term) are contained neatly inside the case.  


How does the SysteMate III work?

A conventional central heating boiler heats the water in the SysteMate III directly. The radiator/boiler pipework is a sealed system with an expansion vessel built into the SysteMate. The boiler is fired and it heats the store by pumping boiler water through a coiled-pipe heat exchanger inside the store. A three port diverter valve switches the pump flow on CH demand to the radiators from either the boiler or the heat store, depending on the temperature of the heat store. When it falls below design temperature the boiler is fired to add heat energy to both rads and heat store.

The SysteMate III delivers hot water to the hot taps by using an external plate heat exchanger and a further pump. The pump starts when a hot tap is turned on and pumps hot store water through the plate heat exchanger, thus heating the cold mains water very effectively on it's way to the hot taps or showers.


Faults known to occur in the SysteMate III:


1) Circulating pump failure

Even SysteMate IIIs are all quite old now, and many of those without corrosion inhibitor in the circulating water are suffering from advanced radiator and system corrosion. The corrosion deposits cause the circulating pumps to seize up and burn out. Fitting a new pump gets the system working again but doesn't address the cause of the original failure. A system cleanse is usually necessary (a 'powerflush'). 


2) Water scale-contamination of the plate heat exchanger.

The plate heat exchanger was hailed my manufacturers as the answer to water scaling, but this has proved not to be the case. Hard water in certain areas still seems capable of blocking a plate heat exchanger with calcium deposits causing restricted hot water flow from the taps and warm (instead of hot) temperatures. The answer now is to fit a repalcement plate heat exchanger, which takes around an hour instead of several hours to descale the previous copper coil heat exchanger. 


3) Blender valve failure.

The thermostatic blender valve is prone to damage from accumulated water scale. This results in the water taps only ever being slightly warm. A new blender valve is necessary.


4) Heat sensor failure.

Hot water temperature from the taps and/or shower becomes unreliable and unpredictable. The hot water temperature sensor delivers a signal to the PSC board and this controls the pump speed. They seem to fail with age (after three or four years) and replacement restores reliable hot water performance. I believe they are thermistors but there is more to them than that as there are three conductors in the leads. Their true nature is shrouded in secrecy. No-one at Gledhill gives anything away when I ask questions... quite frustrating really but I'll get to the bottom of them eventually....!


If you'd like me to come and fix your SysteMate III, contact me now!



First created 22 March 2007
Last updated 10th December 2011