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:
- The PCB first detects the fan is operational, ready to expel dangerous flue gases via the flue
- The gas valve opens to allow fuel to the burner and pilot light
- The spark generator ignites the boiler
- 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
#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.
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.
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.
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.
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.
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:
- Ignition Leads
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.
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.