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Common Grant Boiler Problems


Grant boilers has been manufacturing efficient heating products for close to 50 years. Courtesy of their high-quality products, they have become a favourite brand with many installers and homeowners.

Are you wondering if the life of your Grant boiler has come to an end?

It is true that dealing with a faulty boiler is stressful and a huge inconvenience especially if you depend on it for hot water. And trying to figure out the fault, its urgency and seriousness is tricky.

To help you out, we’ve put together a guide detailing the common boiler faults and their fixes for Grant boilers. With the problems, fault codes, and possible fixes, it’s easier to find the solution.

Note: Not all have DIY fixes. Always call a Gas Safe engineer for complicated problems and fixes.

Boiler will not start

The common cause of this fault includes:

  • Low-pressure cut-out
  • No power
  • Faulty boiler thermostat
  • No gas supplies

Before you call in Gas Safe engineer, you should check the power and inspect other gas appliances to confirm you have a gas supply.


The Gas Safe engineer will inspect the boiler system for faulty components including controls and the thermostat. They will either replace or repair the component depending on the overall condition and which method is economic.

The burner lights but goes out after a while

Usually, this means that theirs is something putting off the flame. It could be:

  • The fan is set to a high speed
  • The fuel tank is empty
  • The burner is faulty
  • The fire valve is closed
  • Malfunctioned flame sensor
  • Blocked gas line

The fan speed should be set at optimal levels to ensure the flame is sustained. Also, when the burner is wet, blocked or faulty, it cannot sustain the flame.


The Gas Safe engineer will unblock the burner and gas line and replace the faulty flame sensor and burner. However, before calling for professional help, ensure you have a gas connection.

Overheat thermostat

Overheated thermostats switch the boiler off. When this happens, your Grant boiler will illuminate a red neon light. The thermostat controls the boiler temperatures and helps to dictate when the heating turns on and off. Users control room temperatures through thermostats.

When the boiler doesn’t turn on and the reset button is not on, then you have an overheated thermostat.


The Grant boiler will not light until you reset the thermostat. To do this, allow the boiler to cool and unscrew the plastic cap. Press the uncovered button and replace the cap.

Low boiler pressure

Boiler pressure fluctuates within a normal 1 bar – 1.5 bar range. But when the boiler pressure suddenly drops it only means there’s a leak in the system. The leak could be in the boiler or in the pipework.

You now you have a pressure problem when the boiler displays an EE2 fault code.


If you haven’t seen a leak yet, increase the pressure by adding water to the system. If the pressure still drops, call a Gas Safe engineer to inspect and seal leaks. They are common in the valves and joints.

Anti-freeze protection

This is a nifty feature in Grant boilers. During winter, the water in the boiler tends to freeze and block the system. This is common with the condensate pipe since it’s outside the building.

The condensate pipe drains acidic wastewater into the drainage system. When it freezes and blocks, the boiler locks out.


This is not a problem to worry about. The PP7 fault code signals that the system is protected from freezing.

High boiler pressure

High water pressure is also a problem for Grant boilers. High boiler pressure puts the boiler components at the risk of damage. High boiler pressure is caused by excess air in the system, pump failure and high pump speed.

Grant boilers display an EE1 fault code.


To reduce boiler pressure, you should bleed the system. This will let out trapped air and release pressure. Be careful not to go below 1 bar.

If this doesn’t work, it means there is a deeper problem. A Gas Safe engineer will inspect the pump for faults and adjust its speed.

No hot water

At times your boiler may not give you hot water but will give heating and vice versa. When this happens, the problem is usually the diverter valve. This valve switches the boiler operation between heating and hot water.

Since it’s a moving part, it’s likely to get stuck between either function. When you don’t receive hot water, it is stuck on heating.


When this happens, the Gas Safe engineer will free the diverter valve or replace it. The diverter valve costs between £250 and £300 including labour costs.

Strange Banging, Gurgling and Whistling

Air trapped in a boiler system causes loud noises. The noises could also be caused by low boiler pressure, limescale build-up or impending pump failure. The type of problem can be diagnosed with the type of noise made. For instance, kettling noise signals limescale build-up.


You can bleed the system without the help of a Gas Safe engineer if you are confident enough. However to Powerflush the system, you should hire a Gas Safe engineer.

Radiators not heating

If some of the radiators are not heating, the boiler could have sludge build-up or an airlock in the system. If the bottom half of the boiler isn’t getting hot, it is ineffective.


Bleeding the radiators will rid the system of the airlock. You can do this without the help of a Gas Safe engineer. However, only attempt it if you are confident enough. The process includes adjusting valves on the radiator.

If bleeding the system doesn’t work, then hire an engineer to perform a chemical flush or a Powerflush.

Room temperature not hitting desired levels

Comfortable boiler temperatures are between 18 and 21 degrees Celsius. However, you can adjust the temperature to suit your needs. If the boiler shuts off before reaching the required temperature, there’s a sludge build-up in the heat exchangers or the radiators.

The temperature sensors pick up on wrong temperatures, send signals to the PCB which shuts of the boiler before the set temperatures are hit.

Also, it could mean the thermostat is faulty.


The Gas Safe engineer will Powerflush the system. They will also get rid of the sludge through a Powerflush or a chemical flush.

Other fault codes and troubleshooting

Fault code PP2 – Discharge gas sensor fault

How to fix: Replace the Discharge gas sensor

Fault code EE3 – Open circuit between terminals 23 and 24 and the PCB

How to fix: Repair the wiring and connections and close the circuit

Fault code EE8 – Communication failure

How to fix: Tighten the wiring and replace faulty boiler parts

Fault code E01 – internal control fault

How to fix: flash the PCM with updated software

How to improve your boilers life?

Grant boiler warranty

To get the Grant boiler warranty, usually 3 years, you need to register the boiler on the online platform within 30 days of installation. Without the registration, you are only eligible for a 1-year warranty. If you use a G-One accredited boiler installer, you can have the boiler warranty extended to a maximum of 10 years. The Grant Warranties cover the labour.

However, faults as a result of tampering or accidental damage are not covered under the warranty. And to maintain the warranty, you need to conduct annual boiler servicing.

Grant boiler service

Gas boiler engineers conduct boiler services to check performance, efficiency and safety. Annual boiler services ensure you get the best out of your boiler and that the boiler warranty is maintained.

During an annual service, the engineer will:

  • Clean the boiler parts
  • Check the boiler parts for wear and tear
  • Test the boiler efficiency
  • Grant boiler cover

When your Grant expires, you can buy boiler insurance to protect your boiler. However, read the details of the boiler insurance before buying.

Finding trusted boiler engineers doesn’t have to be hard. Call us today for multiple boiler service and repair quotes. If you need a new boiler installation, we shall provide you with the best boiler installer as well.

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