(Firstly, most Boilermates are qualified with II, III or 2000 or similar suffixes. The first, original BoilerMate was just called a BoilerMate without suffix. This page deals with the BoilerMate II)

How does the BoilerMate II work?

A conventional central heating boiler heats the water in the BoilerMate II 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 left-hand pump circulates the stored hot water around the radiator circuit(s) when the heating controls are calling for heat. 

There are two circuit boards behind the cover panel. 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.

The BoilerMate II differs from the previous BoilerMate (original) in that it has a user-adjustable thermostat for the heat store. This feature allows the user to control the temperature of the heat store but was dropped from later versions, probably due to user-confusion about how to use it. Good thing too as even I can't explain clearly and simply how to set it! (Just follow the instructions written next to the dial.)

Heat is transferred into the hot tap water by passing the 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 mixes in a proportion of cold water. The output temperature can be set by the user.

Faults known to occur in the Boilermate II:

1) Depleted water in the thermal store.

BoilerMates have a filling, or top-up tank fitted to the top of them, which is there to fill the unit with water. This may or may not have a float valve connected to the mains water supply to fill it. When there is NO mains connection, there is usually provision for manual filling by the user by means of a tap on the wall nearby. When the user doesn't realise this, water lost from the thermal store through evaporation and/or leaks can prevent the unit from working. If the water level falls too low, the heat exchanger coil ceases to be immersed in stored hot water so when a hot tap is turned on, the unit will not deliver hot water. The answer is to check the water level in the top-up tank and top it up to the waterline embossed into the wall of the cistern. This problem is usually accompanied by a noise of water trickling or flowing inside the unit. This is caused by the flow from the boiler discharging into the unit above the water level inside and making the 'pouring' noise. This can be very bad for the system as accelerated corrosion usually results from the constant aeration/oxygenation of the circulating water.

2) Blocked internal cold-fill pipe

The top-up tank fills the main water store via an internal pipe leading down to the base of the unit. On the BoilerMate II specifically, this pipe is prone to blockage with products of corrosion. It it usually impossible to clear in my experience and the best solution is to install a new, external cold fill pipe. The unit must first be fully drained. A hole is drilled through the wall of the top-up tank and a tank connector fitted. The drain tap at the bottom of the unit is removed and an adaptor fitted to the hole to connect a copper tube. A copper tube is then fitted externally from this adaptor up to the new tank connector, with a new drain point fitted into the tube near the bottom. The unit can then be re-filled and re-commissioned.

3) Circulating pump failure

BoilerMate IIs 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'). 

4) Water scale-contamination of the coiled-pipe heat exchanger.

The coiled-pipe heat exchanger is extremely prone to water scaling. This presents as maximum water temperature becoming progressively lower, and in the final stages of scaling, the flow rate from the taps reducing to almost zero. Chemical descaling is the only answer, using  conventional descaling chemicals and techniques. 

5) 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.

6) Thermostat failure.

 The unit fails to heat up properly, leading to warm or cool water from the hot taps and warm and cool radiators at the same time. A new thermostat fixes it.

If you'd rather I came and fixed your BoilerMate II, contact me now!