Servicing a regular boiler with a hot water cylinder

In inner London most flats have combis. Head out to the suburbs and things change. In Bromley, Beckenham, Orpington, Purley and similar areas, many interwar and Edwardian family houses still run a regular boiler with a hot water cylinder and tanks in the loft.

How a regular system works

A regular boiler, also called heat only or conventional, heats water for the radiators and for a hot water cylinder. It does not heat tap water directly.

Part	Where it is	What it does
Regular boiler	Kitchen, utility, garage or loft	Heats water for radiators and cylinder
Hot water cylinder	Airing cupboard	Stores hot water for taps
Cold water storage tank	Loft	Feeds cold water to the cylinder
Feed and expansion tank	Loft	Tops up the heating and gives room for expansion
Pump	Near boiler or cylinder	Moves water round the system
Motorised valves	Near cylinder	Direct heat to radiators, cylinder or both
Cylinder thermostat	Strapped to the cylinder	Tells the system when stored water is hot enough

Because the system is open to the air through the loft tanks, it is called open vented.

What the service covers

The boiler

The core checks are the same as any gas boiler: gas pressure, burner, heat exchanger, seals, electrodes, flue and a combustion test with a flue gas analyser. Older regular boilers may be non condensing and have different parts from modern models.

Pump and valves

The engineer checks the pump is running and the motorised valves open and close correctly. A sticking valve is a common cause of hot water but no heating, or the other way round.

Cylinder controls

The cylinder thermostat is checked. If it fails, water can be too cool or too hot. Stored hot water should be kept hot enough to control bacteria.

Loft tanks

Where access is safe, the engineer checks:

• The cold water tank lid fits and the water is clean
• The float valve shuts off properly
• The feed and expansion tank has the right water level
• The overflow pipes are clear

Bromley houses and these systems

Bromley is the largest London borough by area and has many larger semis and detached houses built between the wars. These homes often have more radiators, longer pipe runs and bigger cylinders. Our Bromley area page covers the housing.

Bigger open vented systems collect more sludge. Air and fresh water get drawn in through the loft tank over the years, which causes rust inside radiators. Signs are radiators cold at the bottom and a boiler that sounds louder than it used to. Ask about a magnetic filter clean and health check at the same visit.

Hard water and cylinders

Most of Bromley is supplied by Thames Water, which says all the water in its region is hard. In a cylinder, scale builds up on the coil inside, the part the boiler heats. A scaled coil means the cylinder takes longer to heat up. If your hot water takes much longer to recover than it used to, mention it at booking.

Loft boilers

Some regular boilers are in the loft. If yours is, the engineer needs:

• A safe, fixed or sturdy ladder
• Boarding to stand and kneel on
• A working light
• Clear space around the boiler

In winter, condensate pipes from condensing boilers in lofts or garages can freeze. See our post on frozen condensate pipes.

Common faults found at service

Fault	Symptom
Sticking motorised valve	Heating or hot water not working
Failing pump	Noisy, radiators slow to heat
Faulty cylinder thermostat	Water too hot or too cool
Sticking float valve	Overflow dripping outside
Sludge	Radiators cold at bottom
Scaled cylinder coil	Slow hot water recovery

Repairs are priced after the engineer has found the fault.

Should you switch to a combi?

A combi removes the tanks and cylinder, which frees space. But a combi supplies hot water to one or two taps at a time, at a rate limited by its size and your mains pressure. A family house with two bathrooms may be better with stored hot water, perhaps a system boiler and unvented cylinder. See our post on system boiler service.

A service is about keeping what you have working well. If you are thinking about a change, the engineer can give a view.

Booking

When you book a system and regular boiler service, tell us:

• The boiler make and model
• Where the boiler, cylinder and tanks are
• How to get into the loft
• Any problems with heating or hot water

Gas work in the UK must be done by a Gas Safe registered engineer. Ask to see the ID card and check it on the Gas Safe Register.