Boiler Gas Valve – Failure, Faults and Replacement Cost

In this 3-minute guide, we’ll explain how a boiler gas valve works, common gas valve problems you may encounter, as well as the potential replacement and repair costs.

What Does a Boiler Gas Valve Do

A boiler gas valve controls the flow of gas to the pilot light and burner. It’s controlled by an electrical signal coming from the printed circuit board (PCB).

When you call for heat or hot water on a gas boiler, the process works like this:

1. The PCB detects that the fan is operational, ready to expel dangerous flue gases via the flue
2. The gas valve opens to allow fuel into the burner and pilot light
3. The spark generator ignites the boiler
4. The flow of gas continues until the PCB recognises that the NTC thermistor (flow sensor) has reached the desired temperature

The Top 4 Gas Valve Faults and Gas Valve Troubleshooting 

Below, we’ll walk you through the most common boiler gas valve faults and fixes.

#1 – Valve Seized or Stuck

The most common boiler gas valve problem is when the valve has become stuck or seized.

Like any mechanical component, a gas valve wears out over time. When the valve gets stuck or seized, it will either:

• Not open, and therefore cut off the gas supply to the burner and pilot light
• Not close, so gas will be letting by even if you’ve turned heating and hot water off

When this happens, your boiler will show a fault code. For instance, the Vaillant F62, Worcester 234, or Baxi 133.

The Fix

In some cases, a Gas Safe engineer will be able to free the valve.

Then, they’ll reset the boiler and test the valve — if it’s fully operational, you won’t need to replace it.

#2 – Wiring Or Connection Problem with the Gas Valve

All electrical components on a boiler, gas valve included, send and receive signals to the PCB (Printed Circuit Board).

Without communications with the PCB, these components don’t know what to do next and the PCB doesn’t know what they’re doing currently.

As boilers vibrate, they can work wiring and connections loose. This often generates weak (or incorrect) signals and leads the PCB to think the gas valve is on or off when it isn’t.

The Fix

A Gas Safe engineer will check the wiring and connections to and from the PCB using a multi-meter; there’s a good chance a connection is loose.

Once these loose connections are reattached and the boiler goes through a reset, the signals will return to normal.

#3 – Faulty Boiler Gas Valve

Unfortunately, not all boiler gas valve problems have a simple fix.

If your boiler is 5 years or older (especially if it’s from a lower-quality brand), the valve is likely beyond repair.

The Fix

Before completely writing off the valve, a Gas Safe engineer will be able to check the wiring, connections, and operation of the valve.

If it’s in poor condition, there are repair and reconditioning kits for gas valves that may help.

However, the time and cost of these kits usually means replacing the valve is a better option. Your boiler care policy should cover the replacement cost, but if you’re not covered, you’ll end up spending £300 or so out-of-pocket.

#4 – PCB Failure

Most boilers have a basic fault code system.

Any fault code that relates to an electrical part (such as the valve) might not be as accurate as you think.

When electrical faults are present, the PCB can’t be ruled out as the culprit. After all, it’s the PCB that controls these components and displays the fault code in the first place.

The Fix

As your engineer will already be testing the boiler’s valve with a multi-meter, it makes sense to test the PCB, too.

We’ve been to properties where the engineer has jumped to conclusions and replaced the gas valve.

Whilst the valve was at fault, the PCB was too.

The PCB then needed to be replaced at an additional cost.

Gas Valve Replacement Costs

Gas valves cost around £300 to replace, including parts and installation.

However, whereby replacement boiler spares can be purchased from the likes of Honeywell, this price can be reduced (they sell some gas valves for under £90).

On the flip-side, if you must go with an OEM gas valve from a brand like Worcester Bosch, the part alone could cost in excess of £150. Speak to your engineer and see if there’s a non-OEM (but high quality) gas valve, like Honeywell, that’s compatible with your boiler.

On a side note: Always ensure your Gas Safe engineer inspects all the most expensive boiler parts before replacing the valve. If 2-3 expensive parts in a boiler are worn, it makes sense to invest that cash into a new boiler, not waste money on repairing an old one.

Expensive parts besides the gas valve include the:

• Burner
• Heat exchanger
• PCB
• Ignition Leads
• Fan
• Pump

Gas Valve Cost to Repair

The cost to repair the gas valve on your boiler will depend on what’s wrong with it.

If it’s a case of simply freeing a valve that’s stuck, the repairs costs could be less than £100.

For any severe issues, however, we rarely find that the repair costs are justified — especially if the unit is already showing signs of wear. Investing in boiler replacement is generally the wiser choice if your boiler’s repairs are mounting and it’s out of warranty.

What’s Next?

Thanks for reading our gas valve guide. Got other boiler problems not mentioned above? Leave us a comment below, and we’ll get back to you as soon as we can.