Gledhill BoilerMate Problems: No Hot Water or Lukewarm
Most Gledhill BoilerMate problems come down to one question: is the store hot? A BoilerMate is a thermal store. The boiler heats a tank of heating water, and your mains water is heated on the way to the tap as it passes through a plate heat exchanger, pushed by a small pump. If the store is cold, the fault is on the heating side: the boiler, its controls, or the sensor that tells it to fire. If the store is hot but the taps run cold, the fault is on the hot water side: usually the pump, the flow sensing or the control board that runs them. Lukewarm or fading hot water, especially in hard London water, is very often a scaled plate heat exchanger. Water under the unit needs tracing before anyone talks about replacing the store. All of these are repairable by an engineer who knows thermal stores, and many general plumbers will not touch them.
How a BoilerMate works, in two sentences
The big tank inside the casing holds heating water, not the water you wash in, and it is kept hot by your gas boiler. When you open a hot tap, the unit senses the flow, starts a pump that pushes hot store water through a plate heat exchanger, and your mains water picks up the heat on its way through the other side of the plate.
That is why a BoilerMate gives mains pressure hot water without a pressurised cylinder, and why it has a control panel, a pump and a small tank on or in the unit that tops the store up. It is closely related to the Gledhill Pulsacoil, which works the same way but is heated electrically. Our guide on how a Pulsacoil works goes into the principle in more detail, and our Gledhill cylinders explained page shows how to tell the ranges apart.
Step one: feel the store
Carefully put your hand on the casing near the top and then near the bottom. If the panel comes off easily, feel the pipes coming out of the top of the store instead. You are looking for hot, warm or stone cold. This one check splits almost every BoilerMate fault into two groups and it is exactly what an engineer does first.
- Cold store, and the radiators are cold too: the boiler is not heating anything. Look at the boiler display for a fault code and check its pressure or power first.
- Cold store, radiators fine: the store is not calling for heat, or the heat is not getting to it. A store sensor, thermostat, valve or control fault.
- Hot store, cold taps: the hot water side. The pump, the flow sensing or the board output that runs the pump.
- Hot store, lukewarm taps or water that fades: a scaled plate heat exchanger, a blending valve fault, or a store that is not getting hot enough.
No hot water with a hot store
Open a hot tap and listen at the unit. You should hear the pump start within a second or two. If nothing happens, the pump is not being told to run, or cannot run. Pumps seize, particularly after a long spell of little use such as a summer away, and some hum without turning. The flow switch or sensor that tells the board a tap is open can also fail, and so can the relay on the board that switches the pump.
The control board is the most expensive single part and gets blamed too early. It should be condemned only after its outputs have been measured and found dead. A pump that runs but gives only lukewarm water points past the pump, to the plate.
Lukewarm hot water, or hot that goes cold
The plate heat exchanger has narrow channels, and the mains water side scales up over the years. In hard London water this is one of the most common BoilerMate complaints. The first sign is that hot water is fine at a trickle and disappointing at full flow. Later it is disappointing at any flow. The plate can often be descaled or replaced, and our guide to hard water and hot water cylinders in London explains why scale is such a problem here.
Hot water that starts well and fades is more often a store that is not reaching full temperature. That can be a boiler that is not firing for long enough, timer settings that have changed, or a store sensor that reads wrongly and tells the boiler the store is hot when it is not.
If the whole house has also lost heating, see our guide to no heating or hot water, because the boiler itself becomes the first suspect.
Leaks, drips and the header tank
Because the store is open to the air rather than pressurised, it is kept topped up from a small feed tank on or near the unit, with a float valve. If that valve sticks, water runs out of the overflow or the vent. A dripping overflow pipe outside, near where the BoilerMate sits, often starts there, and it is a small repair. Our guide to a header tank overflowing covers the same float valve fault on conventional systems.
Water on the floor under the unit can come from the float valve, a weeping pump, a joint on the plate heat exchanger or a leaking store. They look the same on the carpet. The store body is the one part that cannot sensibly be repaired, so it is worth tracing the leak properly before anyone recommends a replacement.
If you can see water near the control panel or electrical connections, switch the unit off at its isolator and at the consumer unit before you do anything else.
Checks you can do before you call
These are safe and quick, and they answer the questions an engineer will ask first.
- Check the boiler is on, has power, shows no fault code and, if it has a gauge, has pressure.
- Check the switches and fused spurs near the BoilerMate and the boiler are on, and that nothing has tripped at the consumer unit.
- Check the timer or programmer settings have not changed, for example after a power cut.
- Feel the store top and bottom and note hot, warm or cold.
- Open a bath tap, not the shower, and listen for the pump.
- Photograph the data plate, usually on the front panel or inside the door, and any lights on the control panel.
Repair or replace?
Most BoilerMate faults are individual parts: a pump, a sensor, a float valve, a plate or a board. Parts availability varies with the age and model, which is why reading the data plate matters before promising a repair. A unit with a sound store and a failed pump or plate is normally worth repairing.
Replacement starts to make sense when the store itself is leaking, when the parts for your model are no longer obtainable, or when the unit is too small for how the household now uses hot water. The usual alternatives are an unvented cylinder with a system boiler, or a combi. Our guides to unvented cylinder installation and converting to a combi boiler set out what each involves, and an engineer who has looked at your system can tell you which suits it.
When to call us
We work on BoilerMate units under our Pulsacoil repair service, because the pump, plate, sensors and controls are closely related, and many engineers turn thermal store work down. Call us on 020 4652 5111 or send an enquiry with a photo of the data plate and the control panel, and tell us whether the store feels hot. We have 20 engineers across London, and our rate is on the pricing page and agreed before anyone attends. If the boiler is showing a fault, our boiler diagnosis visit covers that side in the same trip.
Questions we get asked
- Why is my Gledhill BoilerMate not giving hot water?
- Feel the store first. If it is cold, the boiler or the controls that tell it to heat the store are at fault. If it is hot but the taps run cold, the pump, the flow sensing or the board that runs the pump has usually failed.
- Why is my BoilerMate hot water only lukewarm?
- Most often the plate heat exchanger has scaled up, which is common in hard London water. It can also be a store that is not getting fully hot because of the boiler, the timer or a faulty store sensor.
- Is a BoilerMate the same as a Pulsacoil?
- They are closely related Gledhill thermal stores and work the same way at the tap. The difference is how the store is heated: a BoilerMate by a boiler, a Pulsacoil by electric immersion elements.
- Can a Gledhill BoilerMate still be repaired?
- Usually, yes. Pumps, sensors, float valves and plate heat exchangers are replaceable, and boards depend on the model. The store body itself cannot sensibly be repaired if it leaks.
- Why is water coming out of the overflow near my BoilerMate?
- The float valve on the small tank that tops up the store is probably not shutting off. It is a small repair, but get it done, because the store keeps taking in fresh water while it runs.