Central Heating Repairs: Easy to Follow Guide


Although water-filled (‘wet’) central heating systems vary widely in design, most work on the same basic principle and share the same basic problems. The majority of faults are easy to trace, and many can be put right without specialist knowledge or tools. But even if you don’t fancy making your own repairs, knowing where the trouble lies can significantly reduce the cost of calling in a professional.

The repairs in this section cover the system — pipes, boiler, radiators and so on. The following section deals with repairs to the electric controls — programmer, room thermostat and control valves.

anatomy ofa central heating system



Most people prefer to leave boiler repairs to an expert, but there are simple checks which you can make to pinpoint trouble spots.

If the pilot light is working, a sudden breakdown could be nothing worse than a blown fuse in the plug or FCU supplying the boiler. If the fuse is OK, check the electrical controls.

If the pilot light isn’t working, switch off the supply and — if you haven’t already done so — open the casing.


Pilot light problems

The pilot light unit is located at the foot of the boiler, directly in front of the burners. On most boilers there is an inspection hole to check the flame, but you may have to remove a screw-on cover to get a better view of the unit itself.

In most boilers the pilot burns permanently. When the programmer switches on the main gas supply to the burners, it is the pilot which lights them. But if the pilot goes out for any reason, a heat-sensing device called the thermocouple shuts off the gas supply to prevent leaks.

A pilot light which goes out may not relight for three reasons:

Faulty igniter Some boilers have a piezo-electric igniter, similar to those on gas hobs. On most models you can check if this has failed by holding down the igniter button and lighting the pilot by hand. If the pilot works, the igniter is faulty.

Faulty thermocouple When this fails, it shuts off the gas supply to the pilot light permanently. The cure is to have the thermocouple replaced.

Blocked gas jet If the pilot light only lights with difficulty, or splutters and burns feebly, the chances are the gas jet is blocked. Have the unit cleaned and adjusted.


Thermostat problems

Erratic temperature control of the system water (which in turn affects the heat of the radiators and tap water) points to a faulty boiler thermostat.

First, identify the thermostat dial, and the copper sensor tube which runs from the thermostat to a pocket in the heat exchanger.

♦ Check setting on the dial. Unless otherwise specified, it should be at least 65°C (160°F) — or between 7-9 if the dial doesn’t show temperature.

♦ Check that the phial-shaped end of the heat sensor tube is securely located in the heat exchanger.

If all seems in order, the thermostat itself is probably faulty and must be replaced.


Getting help

The parts above are simple for an engineer to replace. Make things easier still by telling him what you think is wrong over the phone, and giving him the make and model number of the boiler.

To avoid future problems it’s worth entering into an annual service contract. In the UK, check that the contractor is a member of CORGI (the Confederation Of Registered Gas Installers).


Other systems

The instructions given here apply to most types of gravity and fully pumped systems. However, they exclude:

♦ Pressurized (unvented) systems, which are now allowed under the Building Regulations and found in some recently built homes.

♦ Combined systems (eg. Vaillant Combi) in which the boiler and hot water storage are combined in a single compact unit.

Both these systems require expert maintenance.


Turn off the power

Always turn off the power supply to the boiler and programmer (which automatically switches off the heating) before carrying out any repairs. If there is no separate plug and socket or fused connection unit (FCU), switch off at the fusebox.

26. May 2011 by admin
Categories: Heating, Plumbing | Tags: , | Comments Off on Central Heating Repairs: Easy to Follow Guide


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