Introduction
When the circulating pump is first installed it will have (should have) been set up to best match the requirement of the central heating and hot water system. As the system settles down there may be occasions when the circulating pump speed needs to be adjusted e.g. new radiators fitted, property extension/room conversion or possibly due to system corrosion. If it is due to system corrosion then the sludge, rust and debris need to be removed and the system protected . It may be that the circulating pump is reaching the end of its working life and needs replacing.

Many circulating pumps have a manual speed selector (usually 3 speed settings) which allow for adjustment of speed to match the requirements of the system. In other words, the speed at which water will be circulated through the system without creating flow noise (due to excessive velocity), provide for an adequate flow over the boiler heat exchanger (to prevent kettling and damage), provide quick warm up of radiator temperatures yet give the correct flow and return temperature differentials for maximum efficiency. With good design practice and installation the recommended maximum water velocity is 2 metres/second regardless of pipe diameter. If the water velocity is kept to approximately 1.0 metres/second for small bore and 1.5 metres/second for micro-bore systems problems with noise, erosion, corrosion or cavitation should not arise.

Setting Pump Speed
The best speed setting will provide adequate circulation and provide the correct flow and return temperature differentials appropriate to the boiler. This will achieve maximum economy and efficiency.

1. Set the speed selector to maximum (three). Set the programmer to ‘CH’ on
2. Open all thermostatic radiator valves or manual radiator valves to maximum
3. Set the room thermostat to maximum
4. The boiler and pump should start
5. After 10 minutes turn the circulating pump speed selector to minimum (one)
6. Wait another 10–15 minutes and if the radiators are not hot turn the circulating pump speed selector to
    the mid-setting (two)
7. Wait another 10–15 minutes and if the radiators are still not hot set circulating pump speed selector to
    maximum (three)

Note:
a) If the speed setting is too high water noise may be a problem
b) If the radiators get hot at different intervals the radiator system requires balancing

Alternatively, fit an automatic and fixed speed circulating pump.