Page 10210.2.5 Pressure Relief ValveAny pressure relief valve fitted to the boiler or system must be able to discharge externally to adrain where the discharge can be seen but cannot cause any injury or damage. No other valvesshould be positioned between the relief valve and discharge termination. The pressure reliefvalve should be manually activated periodically in order to assess valve opening, normally aspart of servicing.10.2.6 Low Pressure SwitchWhere there is a catastrophic loss of water from the system the boiler thermostats may fail tooperate which would result in serious damage to the appliance. To prevent this it isrecommended that a low pressure cut out switch set at 0.3 bar is fitted to the system and wiredin series with the boiler limit thermostat. Combination Boiler models are factory-fitted with a lowsystem pressure shutdown as standard.10.3 Combination Boiler Domestic Hot Water10.3.1 Mains Water PressureTo protect the appliance and to prevent excessive flow rates, a pressure reducing valve isfactory-fitted to limit the maximum supply pressure to 3 bar.A mini expansion vessel is factory-fitted after the pressure reducing valve in order to protect theappliance from the expansion due to heating of the water in the domestic hot water pipework.Depending on DHW system volume, additional expansion may be required.We strongly advise that all installation pipework is run in copper. However, if plastic pipe orplastic coated pipe is used, it must be recommended by the pipe manufacturer for use with oilfired appliances and, in any case, the last 1000mm of pipework connected directly to theappliance must be of copper.Note that the flow rate from individual taps is dependent on the number of outlets beingoperated together, as well as the length and size of pipework and the mains supply pressure.10.3.2 Water HardnessAlthough many of the DHW components are designed to resist lime scale formation, in areas ofhard water it may still be necessary to fit an inline chemical water softener. For furtherinformation contact Warmflow and your local water company.10.3.3 BoreholesIn order to minimise the pressure variations it is recommended that the differential setting on theborehole pump pressure control is kept as low as possible without adversely affecting the pumpmotor. The accumulator must be as large as possible in order to reduce the rate of pressurechange and a pressure reducing valve (PRV) must be situated between the pump andaccumulator and the boiler. The PRV must be set slightly below the minimum setting of thepressure switch on the pump.
