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Boiler Gas Valve – Failure, Faults and Replacement Cost

In this 3-minute guide to boiler gas valves we’ll quickly explain how these valves work, common problems, as well as the potential replacement and repair costs.

What A Boiler Gas Valve Does

The gas valve on your boiler 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 demand heat or hot water, the boiler works like this:

  1. The PCB first detects the fan is operational, ready to expel dangerous flue gases via the flue
  2. The gas valve opens to allow fuel to 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
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The Top 4 Gas Valve Faults

#1 – Seized Or Stuck

The most common boiler gas valve problem is one that’s stuck or seized.

Like any mechanical component, over time they will wear.

When the valve gets stuck or seized it will either:

  • Not open, and therefore not supply gas to the burner and pilot light
  • Not close, and 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.

The valve needs to be tested after the boiler is reset. If it’s fully operational, a replacement won’t be needed.

#2 – Wiring Or Connection Problem

All electrical components on a boiler send and receive signals to the PCB.

Without these signals, they 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 creates weak (or incorrect) signals and the PCB may think the gas valve is off (and vice-versa), even when it isn’t.

The Fix

An 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 secured, the signals will return to normal after a boiler reset.

#3 – Faulty Unit

Not all boiler gas valve problems are a simple fix.

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

The Fix

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

There are repair and reconditioning kits available for boiler gas valves.

However, the time taken and the cost of these kits usually means replacing the valve is a better option.

#4 – PCB Failure

Most boilers have a basic fault code system.

Any fault code that relates to an electrical part (such as the gas 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 gas 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.

Taking that into account, the homeowner would have been much better off installing a new boiler with a long warranty that covers expensive repairs like this.

Gas Valve Replacement Costs

Boiler gas valve replacement costs are usually determined by the cost of the valve itself.

A typical gas valve replacement price will be around £300 including parts and installation.

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

On the flip-side, if you must go with an OEM valve from the likes of Worcester Bosch, the valve 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 engineer inspects all the most expensive parts of the boiler, 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 an old one.

Expensive parts besides the gas valve include the:

  • Burner
  • PCB
  • Ignition Leads
  • Fan
  • Pump

Gas Valve Repair Costs

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 the valve due to it being stuck open/a closure fault; this could be less than £100.

However, we rarely find that the repair costs are justified, considering the unit is already showing signs of wear.

What’s Next?

Thanks for reading our 3-minute guide to boiler gas valves.

Got other boiler problems not mentioned above? Refer to our guide to boiler fault finding.

And, if you’ve got any questions about gas valves, leave a comment below.

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  1. Can a gas valve be fixed if water got inside? Done an multi meter test an the soilends still working. Obviously dried it out but only firing for few second s before cutting out. Thanks

  2. Hi, we have a Greenstar 30i boiler and when it comes on/goes off the noise that the valves make can be heard around the house.
    This is extremely annoying as it constantly wakes us up during the night, even though we’ve changed it to Eco setting.
    The turning on/off at random times is being looked at by our gas engineer (he’s been round about 5 times now) and a new thermostat has been ordered, but can you offer any advice on why the valves are so noisy please? It’s driving us nuts

  3. Hi – My 3 yr old Vaillant LPG ecotec seems to be working fine (no fault codes showing) except the gas valve is making a slight tick-tock sound, sometimes almost as regular as a clock, sometimes quiet for several seconds. Is that normal or is there some problem developing? It may always have done that but I only just noticed it when topping up the water.
    Might be relevant that because we have a couple of a/a heatpumps doing much of the heating, the boiler spends most of its time at a low output to a reduced radiator system. Not doing DHW either.
    Your thoughts much appreciated!

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