Boiler problems you can tackle yourself

If you're having problems with your boiler, try troubleshooting with this handy do-it-yourself guide. You might find that it's a simple fix or clean that's necessary rather than a full service.

Hot water on demand

If you can manage without stored hot water, choose a combination boiler. This provides water for the heating system in the same way as a traditional boiler, but heats up water for washing on demand.

It can be expensive to repair, however, and suits a small home better than a large one with high water consumption.

 

For greatest efficiency

If you want the best possible fuel efficiency, select a condensing boiler, which extracts heat from the flue gases.

It can heat water for instant use or for storage and is less complicated and more reliable than a combination boiler.

Read more: How to drain your central heating system

 

Check out the flue

A boiler with a balanced (room-sealed) flue must meet the requirements of the current Building Regulations. These govern how close the flue outlet can be to the corners of the building, to walls opposite the flue outlet, to any opening windows and to overhanging eaves.

 

Oil-fired boilers

Consider an oil-fired boiler if you don’t have mains gas. Made in traditional, combination and condensing versions, they are connected to open or roomsealed flues.

They are cheaper to run than gas boilers but servicing costs are higher, and you have to provide safe, approved storage facilities for the fuel.

 

Reduce scale in the system

Boiler problems

In hard-water areas, scale gradually builds up on the heat exchanger inside a boiler and this will eventually reduce its efficiency.

You can prevent it by fitting a self-dosing phosphate scale inhibitor on the supply pipe from the feed-and-expansion tank to the boiler circuit pipework.

The cartridge needs replacing about once a year.

Read more: How to use less water in the bathroom

 

Check the light

If a boiler stops lighting, check that the pilot light is on, or comes on when the ignition sparks at the start of the lighting sequence. Open the front panel to get at the spark generator button if you can.

Following the instructions on the inside of the panel, press in the control knob on the gas valve and try to light the gas by pushing the button. You should see the spark through the observation glass.

 

Sleeve the lead

If pressing the spark generator button doesn’t create a spark, check that the lead from the spark generator to the electrode is not shorting out.

The tiniest spark shorting across from the lead to the body or casing of the boiler will impair the ignition. Rearrange the lead so it is away from the casing, or cover it with a piece of heat-resistant sleeving, sold in electrical shops for insulating cable cores in enclosed light fittings.

 

Safety first: The Gas Safety Regulations state that it is illegal for anyone to carry out any work in relation to a gas fitting who is not ‘competent’ to do so.

This means that in practice you should leave all but the most simple boiler servicing jobs to a qualified gas fitter who is on the register of CORGI (Council for Registered Gas Installers).

 

Leave jets alone

If you have a spark but the pilot light won’t ignite, you may have a blocked gas jet. The boiler will need expert servicing. Don’t try to clean the jet with a pin, because this will over-enlarge the hole and cause the flame to soot up.

If the flame lights but will not stay lit, suspect a faulty thermocouple—the safety device that shuts oƒ the gas flow to the burners if the pilot light goes out.

Read more: Solve your central heating problems

 

Adjust the flame

Adjusting the boiler flame

Some boilers have a clearly marked and easy-to-operate adjusting screw which can be turned to change the size of the pilot flame. Adjust it so the flame just covers the tip of the thermocouple probe.

Do not have the pilot light set so high that the flame appears to be detached from the gas jet.

 

Universal thermocouple

Universal thermocouple

If the pilot light goes out when you release the spark generator button, you need to replace the thermocouple.

Spares are widely available, and a universal model Ïts most boilers. Fitting one is usually straightforward. Undo the nuts holding the old thermocouple (top left), remove it from its tube and slide in the replacement (top right).

 

Stuck switch

A complex electronic management system controls the ignition sequence on fan-assisted boilers. If the fan starts but the boiler doesn’t ignite, the air pressure switch may have stuck and failed to detect the fan running. The switch will need to be replaced, but as an interim measure try switching the boiler off and on a few times to put it through the ignition sequence.

Read more: How to combat damp problems in the house

 

Thermostat tactics

If a boiler switches on and off constantly and there is a room thermostat and a  cylinder thermostat on the system, turn the boiler thermostat up to full and control the room and hot water temperatures with the other two thermostats.

If this doesn’t stop the on/off cycling, ask a heating engineer for advice on having an energy management system installed.

 

Keep up the pressure

If you have a sealed hot water or heating system, check regularly that the water pressure in the system matches the recommendations given by the maker.

Typically the pressure gauge will show about 1 bar when the system is cold, and a maximum of 3 bar (marked with a red line) when it is hot. To raise low water pressure to the correct level, let in water by turning the taps on at either side of the system filling loop.

 

Reset the cut-out

Many boilers have a cut-out that turns the boiler off if it overheats—a fault that can occur if the pressure drops on a sealed system, or the pump stops working on a vented one. Put the fault right if you can (by topping up the system water, for example) and press the manual reset button to restart the boiler. This is usually clearly marked; look for a red button with a cross on it.

If you can’t fix the fault, call a plumber.

Read more: How to fix leaks in the house

 

Pump in some air

If you notice a dribble of water coming from the safety valve outlet on a sealed system, pump some more air into the expansion vessel. This is spherical and usually painted red and is located at the back of the boiler.

Find its air inlet valve (which looks similar to the ones on car tyres), and pump some air in with a bicycle pump or a car foot pump. Measure the pressure with a tyre pressure gauge, or the gauge on the foot pump if it has one.

The pressure needs to be slightly above the cold pressure level on the boiler pressure gauge but below the hot pressure level. This allows water to enter the vessel when the system heats up and its contents expand.

 

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