Mike the Boilerman
Your independent Boilermate specialist based near Hungerford, Berkshire
For more information or to book your breakdown repair, call or text me on
As with all Boilermates, the water stored inside is radiator water, not tap water. A conventional central heating boiler heats the radiator water in the Boilermate directly. The stored water is pumped to the boiler for heating and back again by the right-hand of the two pumps on the unit whenever the stored water temperature drops below a specific temperature set in the factory. The red pump on the right circulates the stored hot water around the radiator circuit(s) when the heating controls are calling for heat. A second pump (barely visible in this photo) below and behind the red pump circulates the already hot stored radiator water around the radiator circuit when the room thermostat calls for heat and the time switch is set to an ‘ON’ period.
There are two circuit boards behind the cover panel. (The cover panel has been removed in the photo above so the circuit boards are visible). A pump drive board to run the central heating pump for a few seconds every forty hours to prevent it seizing up over the summer months when it is not in use, and a delay timer to keep the pump running for a short while after the boiler has shut down to extract the residual heat in the boiler heat exchanger.
For hot tap water, heat is transferred into the tap water by passing cold mains water through a coil of pipe inside the unit, immersed in the store of hot water. Heat passes through the wall of the tube and heats the cold mains water on it's way to the hot tap. To control the temperature of the domestic tap water, a thermostatic blender valve (shown here) mixes in a proportion of cold water. The output temperature can be set by the user by turning the green control knob on the top.
What goes wrong with them?
The Boilermate II (or 2) is the same as the Boilermate original from a plumbing point of view, so if you notice this list seems to be the same as the list for the Boilermate original, you’re right, it is, but I’ve added some photographs to this section.
1) Depleted water in the thermal store:
The hot water is only hot when taps are running slowly, and the unit continuously makes a noise like muffled water pouring. This is usually the store being only partly full of water, usually caused by the float valve in the feed & expansion tank on the top seizing up and stopping working. A new float valve fixes this. Occasionally the same fault is caused by a blocked internal cold fill pipe connecting the F&E tank to the main tank of hot water. The blockage can be extremely difficult to dislodge so with a bit of basic plumbing the blockage is usually best bypassed with a new section of pipe. This photo shows a Boilermate 2 with such an external cold fill bypass pipe, installed in 15mm copper. (I prefer to use 22mm copper as it is less prone to air locking, but 15mm works perfectly well in most cases.)
2) A loud, random, intermittent buzzing noise:
One or other of the two small PCBs makes this noise when it gets old. Best to replace both PCBs in my opinion as I’ve replaced the noisy one occasionally, only for the customer to call me back a few weeks (or hours) later because the other one is shown up to be buzzing too!
3) Hot water failure when heating still works:
The coil of pipe immersed in the tank of hot radiator water is so simple it is hard to imagine how it could NOT always work. But it fails sometimes due to water scale lining the inside of it. Chemical descaling will fix this. The blender valve sometimes breaks giving identical symptoms. Easily replaced with a new one.
4) Pump running continuously:
The gas boiler downstairs shuts off but a pump runs continuously day and night even though the central heating is turned OFF. The noise of the pump is particularly noticeable and annoying in the quietness of the night. There is a little green LED indicator light on the Boilermate 2 front panel, down at floor level. This tells us when the Boilermate 2 is demanding heat from the boiler, which it should not be when the central heating is off. The problem is during heat demand, the boiler-circulating pump runs and if the gas boiler is set to a lower temperature than the Boilermate 2 requires, the boiler circulating pump will run for ever, unsuccessfully trying to heat up the Boilermate. To fix this, simply turn the gas boiler temperature control up to MAX so the Boilermate 2 can get the heat being demanding from the boiler. The Boilermate 2 will turn the boiler OFF once the right temperature has been reached and the green LED should go out and the pump stop. If this fails to work, there is a also summer/winter control on the user control panel of the Boilermate 2. Turn this control fully anti-clockwise to the minimum setting. With this control set to minimum and the boiler at maximum, the green light should go out and the pump noise stop when the heating is off.
When fault-tracing a Gledhill Boilermate 2, the circuit diagram is often useful and although a diagram is on every Boilermate it is easily missed, being printed on a label on the inside face of the tall white cover you remove to get to the internal wiring.
Thats about it really. Not a great deal to go wrong with this simple Boilermate II (or 2). If your Boilermate II (or 2) has stopped working, do call or text me to discuss a repair, on 07866 766364.
Copyright Michael Bryant 2022
Site first created 21st January 2007
Site last updated 2nd April 2022
Gas Safe Register 197499. CIPHE reg no 56207