Central Heating Operation

This article is about Central Heating systems using hot water as a heat-carrying medium. (Warm-air systems are sometimes found in the UK but their design and installation is not covered here. There is a discussion on updating existing warm-air systems here)

The article is about operating an existing, working central heating system.

There are separate articles about:

• Central Heating Design which may help understanding what sort of system you have.
• Central Heating Repair for help diagnosing and fixing a faulty system

This article is a skeleton: the main points to be covered are listed but some or all still need to be expanded

Setting time and temperature controls

• Programmer and room thermostat
  • check there is a room stat
  • check no other sources of heat or valves turned down in stat area
  • better to keep system running or turn up and down?
• Programmable thermostat
  • fully programmable or set-back
  • optimum start (Honeywell issue)
• combis with pre-heat
• setting boiler temperature controls

Setting manual radiator valves

Check the valves on the radiators in the room with the room thermostat are fully open. To turn these valves full, screwing the caps anticlockwise. The temperature in this room is now controlled by the room stat rather than the rad valve.

Adjust rad valves in other rooms to achieve even temperature through the house. With some houses the room temps take a day to stabilise. Little used rooms will generally be adjusted to provide a lower room temperature.

With a new or very maladjusted system, all valves fully open is a good place to start from.

Bleeding a CH system

Bleeding radiators is needed when some of the radiator is hot, but the top is not. This problem is caused by air buildup in the radiators, which is caused by

• corrosion
• sucking in air from the header tank
• or pumping over in the header tank, which oxygenates the water

To bleed a radiator, loosen the little bleed screw at one end of the top of the radiator using a radiator key or pliers. Air will escape with a hiss, when the hissing stops and just water comes out, retighten the screw. Dribbles can be anything from clean water to black, so have a towel ready to catch a little spillage.

The need to bleed any more than very occasionally indicates some sort of problem. Topping up the system corrosion inhibitor solves this in a lot of cases.

Topping up a sealed system

• why? check for how pressure being lost

Protecting system against frost when house empty

Set the room thermostat to minimum or 5 degrees C.