What IS a BoilerMate?:
This page deals with BoilerMates in general. BoilerMates are thermal stores, in other words a tank full of water heated by an ordinary central heating boiler. The water never changes. It is used purely to store heat energy from the boiler. The stored hot water is pumped around the radiators top heat the house, and is used to heat domestic tap water before it arrives at the hot taps. This allows hot water to taps and showers at full mains pressure for high performance showering and faster bath filling.
(The boilermate is very similar to the SysteMate and the two are easily confused. The difference is that the Boilermate pumps the thermal store water around the radiators directly, meaning radiators cannot be installed at a higher level than the BoilerMate cistern. The SysteMate separates the central heating water from the thermal store water using a copper heating coil inside to transfer heat from the boiler primary into the thermal store water, allowing use of a sealed heating system and location of the SysteMate becomes free.)
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. (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 use.
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.
How does the BoilerMate 2000 work?
A conventional central heating boiler heats the water in the BoilerMate 2000 directly. The stored water is pumped to the boiler for heating and back again by the left-hand of the three pumps behind the front panel of the unit whenever the stored water temperature drops below a specific temperature set in the factory. The centre pump pumps water around the radiator circuits when central heating is required.
The BoilerMate 2000 delivers hot water to the hot taps in a similar way to the previous BoilerMate III, but without the user-adjustable thermostatic blender valve. The right-hand 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.
The two separate circuit boards behind the cover panel on the BoilerMate III are now replaced by a single combined control board controlling every function. The appliance Control Board (ACB). There are no user-controllable parameters.
Faults known to occur in the BoilerMate 2000:
1) Depleted water in the thermal store.
BoilerMate 2000s have a filling cistern fitted above 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, eventually there s too little water for the pumps to pump, the unit will make gurgling noises and stop delivering hot water. The answer is to check the water level in the top-up cistern and top it up.
2) Circulating pump failure
BoilerMate 2000s sometimes fail to deliver ANY hot water to the taps at all. After a random amount of time the hot taps start working again. This is usually a sticking hot water circulating pump. The quick fix is to fit a new one, but the underlying cause is usually system corrosion caused by absence of corrosion inhibitor in the initial fill of system water. A powerflush is necessary to prevent the problem re-occurring.
3) Water scale-contamination of the plate heat exchanger.
The plate heat exchanger was hailed by 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. When the problem becomes acute the water flow slows to a trickle and the temperature swings wildly from scalding hot to stone cold. The answer is to fit a replacement plate heat exchanger, which takes around an hour (instead of several hours to de-scale the copper coil heat exchanger in early versions of the BoilerMate)..
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 ACB 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....!
5) Continuous operation of central heating.
The central heating runs continuously, refusing to respond to the room thermostat being turned down or the timer being turned OFF. It's control board failure. A new control board fixes the problem.
