Although the general working operations of your boiler will be explained to you by an engineer, here are some of the features which you may find useful to refer to. Additionally, you can print off our specially created PDF on OSSW Ltd. Filling-Topping Up

(Please Note: your boiler may vary slightly from these examples, but the principle is still the same).

On/Off Switch
Turns the boiler on or off as required. Please note: some boilers are fitted with a ‘Boiler On’ indicator light – check in the User Instructions section of the Installation and Servicing Manual supplied with your boiler.

Control Thermostat
Controls the temperature of the primary water leaving the boiler.

Overheat Thermostat
Automatically cuts the burner out if the boiler overheats. On some boilers, a red light above the reset button indicates if this cut-out has operated. It can be manually reset once the boiler has cooled down.
•    Unscrew the plastic cap and press the reset button (see left). If the boiler overheats regularly, there may be a fault and you should contact OSSW Ltd. on 01837 871 444.

Pressure Gauge
The black pointer on the gauge (see left) should read between 0.5 and1.0 bar when the system is cold. The red indicator can be set to mark this position. The pressure will rise when the system heats up. Excessive pressure on the gauge may indicate a problem therefore, you should contact OSSW Ltd. on 01837 871 444.

Low Pressure Cut-Out (Some Combi Boilers)
Automatically cuts the burner out if water pressure in the system drops below 0.2 bar. An amber light (see left) above the pressure gauge indicates if this cut-out has operated. This will be automatically reset when the system is re-filled or topped-up.

Filling Loop (Sealed Systems Only)
This is to replenish any water loss in your system. The filling loop is either located in the boiler or elsewhere on the system pipework. Topping up will be necessary for example when a radiator has been removed for decorating or air is bled from a radiator. Frequent topping-up may indicate that there is a leak on the heating system or one of its components and may cause internal damage to the boiler and its components therefore, you should contact OSSW Ltd. on 01837 871 444.

Expansion Vessel (Sealed Systems Only)

The expansion vessel (red vessel usually attached to the boiler [see left]) must be checked annually to ensure that there is a 1.0 bar air charge in the vessel. Failure to comply may cause damage to the boiler or system. This is checked on our standard service – please see our service schedule.