BEAMA

General

Many existing central heating systems using regular boilers are of obsolete design and are poorly controlled. Poor design features that should be improved are:

• Gravity circulation to the hot water cylinder - stored water is slow to reheat
• No cylinder thermostat - excessive stored hot water temperatures
• No room thermostat - excessive room temperatures
• No boiler interlock-boiler keeps firing unnecessarily during periods of heating and hot water

Where possible systems should be upgraded to the minimum requirements in the building regulations. Where it is not possible to convert to fully pumped, the following system will provide many of the benefits:

• Cylinder thermostat
• Room thermostat (or programmable room thermostat)
• Standard programmer ( or programmable room thermostat)
• One - 2 port motorized valve fitted on the gravity flow to the hot water cylinder
• TRV's on all radiators except in rooms with a room thermostat
• Boiler interlock

Good and Best Practice

Systems with regular boilers must have separately controlled circuits to the hot water cylinder and radiators, and both circuits must have pumped circulation.

Room thermostats, programmable room thermostats, cylinder thermostats, programmers and time switches must be wired so that they are interlocked with the boiler and pump, i.e. they prevent the boiler from firing when there is no demand for heat.

A bypass circuit must be installed if the boiler manufacturer requires one, or specifies that a minimum flow rate has to be maintained while the boiler is firing. The installed bypass circuit must then include an automatic bypass valve (not a fixed position valve).

Even if there is an automatic bypass valve fitted in the boiler, it is wise to fit another between the flow and return to prevent system noise if the majority of radiators are fitted with TRV's.

Frost protection must be provided where necessary to protect the appliance, system and dwelling.

Radiators in rooms with a controlling room thermostat should be fitted with lock-shield valves on both inlet and outlet connections.