Red Light Flashing on Boiler? Common Reasons & How to Fix It

Red Light Flashing on Boiler? Common Reasons & How to Fix It

The flashing red light on your boiler is an indication that there is a problem with: the fan unit or the air pressure switch or no power going to the fan.

A flashing red light on a boiler is a critical indicator that points to several potential issues requiring immediate attention. Although the precise meaning of this signal may differ depending on the boiler’s make and model, here are some common explanations for why a boiler may display a flashing red light.

What is the flashing red light on my boiler?

Fault or Error

The presence of a flashing red light typically signifies a fault or error within the boiler system. To pinpoint the specific problem, it’s advisable to consult the boiler’s user manual or enlist the assistance of a qualified heating engineer who can decode the error code linked to the flashing red light. Identifying the root cause is essential for taking the necessary steps to rectify the issue.

Low Pressure

Low boiler pressure is a prevalent problem that can trigger the red light to flash. If the pressure gauge on the boiler indicates pressure levels below the recommended range, it can activate the light. Low pressure may result from water leaks, a malfunctioning pressure relief valve, or problems with the filling loop. In such cases, it is essential to top up the system with water or address any leaks to restore the correct pressure.


A flashing red light may indicate that the boiler is overheating. Overheating can occur due to various factors, including a faulty thermostat, a blocked heat exchanger, or issues with the circulation pump. Overheating poses potential safety risks, so it is imperative to shut down the boiler and seek the expertise of a qualified heating engineer to diagnose and repair the problem.

Gas Supply Issues

Another potential cause of a flashing red light is related to issues with the gas supply to the boiler. This can encompass problems such as a gas valve malfunction, gas pressure irregularities, or interruptions in the gas supply. Given the safety implications associated with gas-related issues, it is crucial to engage a professional gas engineer to address and resolve these concerns.

Other Faults

The flashing red light may also point to other malfunctions within the boiler system, including problems with the ignition, pump, fan, or sensors. Such faults necessitate a thorough inspection and repair performed by a certified heating engineer.

It is important to recognise that the flashing red light serves as a warning signal, and prompt action is imperative. To accurately identify and rectify the underlying issue, it is recommended to consult the boiler’s manual or seek professional assistance. This ensures the safe and efficient operation of the boiler, preventing potential hazards and maintaining its functionality.

What Does my Worcester 28Si Mk1 Boiler Flashing Red Light Mean?

The flashing red light on your Worcester boiler is often an indication that there is a problem with:

  1. the fan unit or
  2. the air pressure switch or
  3. no power going to the fan

Should you observe a flashing red light on your boiler, your initial course of action should be to contact a Gas Safe registered boiler engineer. Attempting to address the issue independently could pose safety risks and potentially void your boiler’s warranty.

As a precaution, switch off your boiler and promptly reach out to a qualified engineer who will conduct a series of diagnostic tests, which we’ll outline in the following steps.

Testing the boiler’s fan

Upon the engineer’s arrival, the initial step will be to disassemble the boiler’s casing to gain access to the fan and air pressure switch. This process entails the removal of a screw located at the top of the casing, followed by lifting off the casing itself. Subsequently, the engineer will proceed to detach the combustion cover, which is secured in place by four screws.

Once the combustion cover is successfully removed, the engineer will be in a position to conduct an evaluation of the fan unit. Their first action will involve utilising a multimeter to verify the presence of electrical voltage within the fan’s leads. If the multimeter indicates the presence of electricity in the fan, it serves as an indication that the issue pertains to the fan itself.

Replacing the fan

Should the engineer determine that the fan is defective, it becomes necessary to replace it. Sourcing replacement components for this particular boiler model may pose a challenge due to its advanced age, with only a limited selection of parts still in circulation. Nevertheless, a Gas Safe registered engineer might possess the expertise and resources to locate the required components and perform the necessary repair on your behalf.

Essential troubleshooting tips

When you spot a flashing red light on your boiler, it’s crucial to get in touch with a Gas Safe registered engineer for necessary repairs. Although there are a few initial troubleshooting steps you can take to help identify the issue, it’s imperative to abstain from attempting any DIY fixes. Two common troubleshooting measures involve:

  1. checking the power supply and
  2. monitoring the pressure gauge for potential problems.

In the event of a power supply concern, first verify that your boiler’s power supply is switched on and examine the fuse or circuit breaker for any anomalies. If the pressure gauge indicates levels that are excessively high or low, it may also contribute to the issue. Nevertheless, it’s always recommended to engage a Gas Safe registered engineer to address repairs or maintenance, prioritising the safety of both yourself and your home.