Boiler parts and spares


Boiler parts and spares

by Matthew Knight

If your boiler is broken, our guide to typical boiler parts and spares will help you decide whether it's better to repair or replace your old boiler. 

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A broken or faulty boiler can be an aggravating and potentially expensive problem to fix.

You shouldn't attempt to repair a boiler yourself - you'll need an accredited boiler engineer to complete the work. If you read on, we will help you discover how much different boiler spares, parts and repairs usually cost, to give you an idea of how much you can expect to pay.

You can minimise how much you have to spend on repairs by making sure you have a reliable boiler that won't let you down. To find out which boilers are the most reliable, see our boiler reviews

Common boiler spares and repairs

We asked boiler engineer Adrian Fuller, whose company has been highly recommended on our online Which? Local service, where Which? members recommend local businesses, to say how much common boiler spares and faults cost to repair.

Prices shown below are the range that Adrian’s company in Surrey charged, including parts, labour and VAT. Labour costs will vary, depending on where you live. Costs will also vary depending on your boiler type, age and model. 

Boiler parts and replacement costs

Boiler partBoiler part nameCost to replace part (including installation)What boiler part does
Diverter/zone valvesDiverter/zone valves£118 - £533Directs flow of heated water from the boiler for heating or hot water
Painted circuit boardPrinted circuit board£210 - £434The ‘brain’ – it makes things run together
PumpPump£139 - £389Moves heated water from the boiler, for either heating or hot water
FanFan£203 - £630Moves air through the boiler for combustion
Gas valveGas valve£156 - £554Regulates gas flow to the burner
Overheat thermostatOverheat thermostat£83 - £360Prevents boiler from overheating
Automatic air ventAutomatic air vent£47 - £232Lets air out of the boiler
Pressure relief valvePressure relief valve£98 - £197afety component that ensures pressure does not become dangerous
ThermocoupleThermocouple (only found in older boilers)£57 - £145Essential component in preventing gas leaks if your pilot light goes out
IgnitionIgnition£48 - £139Ignites the pilot/main flame

Boiler spares

The boiler spares are listed in the order that Adrian's team needed to replace them during a 12-month period ending in June 2009. Diverter/zone valves were the most frequently replaced parts and the ignition the least.

Adrian has not needed to replace an expansion vessel in the past 12 months, but this can be quite an expensive component to replace.

The expansion vessel prevents sealed heating systems from becoming over pressurised. In our 2008 research Adrian's company had quoted an average price of £324 for replacing an expansion vessel.

Getting a good deal on boiler spares and parts

You shouldn't attempt to remove the outer casing of your to take a look at what's wrong, so it's unlikely you'll know which spare parts your boiler might need until advised by a professional.

It can be difficult to get hold of boiler spare parts yourself anyway, because many of the reputable spare part retailers and online outlets that sell spare parts for household appliances - websites like Espares or Partmaster, for example - don't offer boiler spares. While several other boiler spares outlets are for trade use only.

Choosing a qualified and reputable boiler engineer is important when getting any work or repairs done. Ask friends and family, or look on Which? Local for recommendations for reliable traders and ask for a breakdown of the quoted costs, including boiler spares, parts, call-out fees, labour and VAT costs.

Boiler services

A regular boiler service should help prolong the life of your boiler and its parts. But you could be better off putting money aside in a cash Isa in the event of having to pay for boiler repairs, rather than signing up for an annual boiler service contract. Adrian's company charges £84 for a full boiler service.

If you want to find out more about boiler servicing, then find out which servicing contracts are rated the most highly by people who use them. See our boiler servicing contract reviews.

Repair or replace?

Determining the so-called tipping point at which it becomes more economical to replace an old, less efficient boiler with a high efficiency A-rated boiler can be tricky given how expensive a new boiler installation can work out. 

But if you're experiencing problems with your boiler and have to pay out for repairs, it could be an opportune moment to weigh up the boiler parts and repairs bill against replacing your boiler, offset by the savings you'll make by switching to a more efficient heating system.

The amount you'll save will depend on the brand, age and type of boiler. You can see typical energy savings calculations by clicking boiler energy efficiency.

Boiler brand parts and spares

If you have decided to get your boiler repaired instead of replaced, it's important to know how your boiler brand operates when it comes to repairs. 

Below we talk you through the repair service for a number of different boiler brands. 

Ideal, Valliant and Worcester Bosch boiler parts

Ideal, Valliant and Worcester Bosch do not sell boiler spare parts to members of the public - only professionals can order boiler parts or download technical specifications for your boiler model. So a boiler engineer will usually obtain or order the correct Ideal, Valliant or Worcester Bosch boiler parts to fix your boiler for you.

Whichever brand of boiler you have, ask for a breakdown of the spare parts your engineer is ordering, and their respective costs including VAT, or ask to see the product catalogue they're ordering from to ensure you're getting a fair rate on the spare parts.

It's also worth taking a look at your Ideal, Valliant and Worcester Bosch boiler manual to check what your warranty covers you for and for how long, as well for contact details for troubleshooting advice.

You can download boiler manuals for current Vaillant models via the Vaillant website. Vaillant also has a technical helpline for homeowners - call it on 0906 802 0251 (calls cost 60p a minute from a BT landline).

For Worcester Bosch you can download boiler manuals via the Worcester Bosch website. Worcester Bosch also has a technical helpline for homeowners - call it on 01905 754 624 (calls cost 60p a minute from a BT landline).

We've reviewed a number of Ideal, Valliant and Worcester Bosch boilers so take a look at our boiler reviews to see which are the most and least reliable boilers. 

Baxi boiler parts

Interpart is the official Baxi spare parts stockist, supplying the industry with Baxi spares and parts. While it does not sell parts directly to members of the public, you can call its enquiry line on 0844 871 1540 if you have a Baxi parts-related question. 

In most cases a boiler engineer will obtain or order the correct Baxi boiler spare or part to fix your boiler for you. As with Ideal, Valliant and Worcester Bosch, ask for a breakdown of the spare parts your engineer is ordering, and their respective costs including VAT, or ask to see the product catalogue they're ordering from to ensure you're getting a fair rate on the spare parts. 

Again, it might also help to consult your Baxi boiler manual for troubleshooting information, or to look up product specifications on the Baxi website. We have also reviewed Baxi boilers, so visit our boiler reviews to see how reliable they are.