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Why my boiler keeps firing when timer or thermostat is off?

Boilers are designed to heat water as efficiently as possible while using the least amount of energy. However, as a result of prolonged use, your boiler may develop issues. Including occasions when the boiler is on, even if the timer is turned off.

Your boiler being on when the timer is off can be due to several issues, including malfunctioning thermostats, valve issues, electrical wiring issues, or other glitches. This can result in massive energy consumption and higher utility costs.

Unfortunately, due to these boiler issues, household energy consumption may become higher than necessary. It is essential to identify the cause of the problem to avoid unnecessary waste. Especially as water heating accounts for a significant portion of residential energy consumption.

Finding and fixing the issues of when your boiler stays on but timer is off

If the boiler keeps running when the programmer is off, then the system needs to be inspected further. A typical control system consists of various components, including a thermostat, programmer, timer, motorized valve, pump, and heating element. One or more of these components could be the culprit.

The system should be evaluated to see what is making the boiler and pump turn on even if the timer is off. The problem of boilers becoming hot even after your heating timer is turned off is more prevalent than you might think, and the following factors can cause it.

1. Valve Issues

Microswitches in the motorized valves regulate the boiler and pump. When the valve is opened, the microswitch is activated, and the boiler begins to operate. However, there are occasions when the valves close while the switch remains in the ‘on’ position. When this occurs, the boiler and pump will startup.

Water valves open and close to allow or prevent hot water from flowing through your water heating system. For example, the diverter valve closes when hot water needs to be sent from the boiler rather than the taps.

On the other hand, check valves are generally closed and automatically open when fluid passes through them. It is typically used for one-way flow and prevents backflow through the valve. A check valve restricts the flow of hot water in one direction, preventing water backflows.

However, because these valves are constantly opening and closing as needed throughout the day, they might become jammed or damaged. When this occurs, hot water will keep flowing through your boilers even if your timer is turned off. 

2. Thermostat Malfunction

A thermostat is like a switch that is activated by temperature. When the thermostat detects that the water temperature is below the predetermined point, it will engage the heating. If it senses a higher-than-set water temperature, it will cut off the heating.

However, your boiler might continue to operate even past that set water temperature. You could start testing this issue by turning your thermostat temperature levels down and then up to see if this makes a difference.

The boiler should turn on more frequently when the temperature rises and cut off when it reaches the desired temperature. If it does not work, you can reset the unit by turning it on and off. If there is no change, we recommend contacting a specialist to diagnose the problem.

3. Wiring Problem

A wiring problem could be the cause of heating coming on when the timer is off. Turn off the power to the boiler by switching off the circuit breaker. This will protect you from electrical shocks. Tinkering with wires can be harmful, so proceed with caution.

To begin, rule out any potential power issues. Next, replace any blown fuses and reset any circuit breakers. Afterwards, check to determine if the electric water heating element or thermostat are receiving power. If the test fails, replace the wire or heating element.

Because checking the wiring might be unsafe, always consult a licensed contractor to handle the problem. During your repair, your contractor may disconnect your boiler from its power supply and inspect its wiring.

4. Boiler comes on when programmer is off

Your boiler will most likely contain either a heating programmer or a boiler timer. A boiler timer will turn on your heating at a specific time each day. Compared to a timer, a programmer can do more and help you make your boiler run more efficiently.

Because many homes are empty during the day, there is little purpose in heating them if no one is around. A programmer enables you to control when the heater comes on and what settings you should have it at, to suit your needs and lifestyle.

The programmer is a control panel that enables you to schedule when your heating and hot water will turn on and off. Here in the UK, programmers are used to save on energy bills and also reduce the environmental impact from boilers. You may be able to select heating, hot water, or both.

The function of programmers varies greatly and will depend on the type of boiler you have. If you’ve had a new boiler installed you’ll most likely have a digital programmer to control your heating.

However, sometimes boiler keeps running when the programmer is off.  One of the causes might be a malfunctioning combi boiler’s single channel programmer. If your using a heat-only boiler, then your two-channel programmer may be the cause.

When these problems occur, the programmer may need to be reset.  To reset your boiler turn off your boiler for 30 seconds and then turn it back on again.

Resetting your boiler usually also resets the programmer.

If that doesn’t work, read your programmer’s user manual for instructions on how to reset it. If you’re still having problems with your boiler programmer and can’t figure out what’s causing the problem, you should get professional help.

Reach out to an expert boiler engineer

If you have any questions concerning your boilers, please feel free to get in touch with us at Boilerchoice. We are always on hand to answer any questions and can even send one of our engineers to take a closer look if required.