Potterton Promax Store 24 Installation And Service Manual page 27

2.7.3 Maintenance Requirements
Unvented hot water systems have a continuing maintenance requirement in order to ensure safe working and
optimum performance. It is essential that the relief valve(s) are periodically inspected and manually opened to
ensure no blockage has occurred in the valves or discharge pipework.
Similarly cleaning of the strainer element and replacement of the air in the expansion vessel will help to prevent
possible operational faults.
The maintenance checks described below should be performed by a competent person on a regular basis, e.g.
annually to coincide with boiler maintenance.
After any maintenance, please complete the relevant Service Interval Record section of the Benchmark Checklist on
page 54 of this document.
2.7.4 Inspection
The immersion heater boss can be used as an access for inspecting the cylinder internally.
2.7.5 Safety Valve Operation
Manually operate the temperature/pressure relief valve for a few seconds. Check water is discharged and that it
flows freely through the tundish and discharge pipework. Check valve reseats correctly when released.
NOTE: Water discharged may be very hot! Repeat the above procedure for the Expansion Relief Valve.
2.7.6 Strainer
Turn off the cold water supply, boiler and immersion heaters. The lowest hot water tap should then be opened to de-
pressurise the system. Remove the pressure reducing cartridge to access the strainer mesh. Wash any particulate
matter from the strainer under clean water. Re-assemble ensuring the seal is correctly fitted. DO NOT use any other
type of sealant.
2.7.7 Descaling Immersion Heater
Before removing the immersion heater the unit must be drained. Ensure the water, electrical supply and boiler are
OFF before draining. Attach a hosepipe to the drain cock having sufficient length to take water to a suitable
discharge point below the level of the unit. Open a hot tap close to the unit and open drain cock to drain unit.
Switch OFF electrical supply to the immersion heater before removing the cover. Open the cover to the immersion
heater housing and disconnect wiring from immersion heater. Carefully remove the thermostat capillaries. Remove
the terminal shroud. Unscrew immersion heater backnut and remove immersion heater from the unit.
A key spanner is supplied with the cylinder unit for easy removal/tightening of the immersion heater. Over time the
immersion heater gasket may become stuck to the mating surface. To break the seal insert a round bladed
screwdriver into one of the pockets on the immersion heater and gently lever up and down.
Carefully remove any scale from the surface of the element. DO NOT use a sharp implement as damage to the
element surface could be caused. Ensure sealing surfaces are clean and seals are undamaged, if in doubt fit a new
gasket.
Replace immersion heater ensuring the (right angled) element hangs vertically downwards towards the base of the
unit. It may be helpful to support the immersion heater using a round bladed screwdriver inserted into one of the
thermostat pockets whilst the backnut is tightened. Replace the terminal shroud. Replace thermostat capillaries into
pockets. Connect wiring to element. Check, and close and secure immersion heater housing cover.
2.7.8 Expansion Vessel Charge Pressure
Remove the dust cap on top of the vessel. Check the charge pressure using a tyre pressure gauge. The pressure
(with system de-pressurised) should be 0.25MPa (2.5 bar). If it is lower than the required setting it should be re-
charged using a tyre pump (Schrader valve type). DO NOT OVER-CHARGE. Re-check the pressure and when
correct replace the dust cap.
2.7.9 Re-Commissioning
Check all electrical and plumbing connections are secure. Close the drain cock. With a hot tap open, turn on the cold
water supply and allow unit to refill. DO NOT switch on the immersion heater(s) or boiler until the unit is full. When
water flows from the hot tap allow to flow for a short while to purge air and flush through any disturbed particles.
Close hot tap and then open successive hot taps in system to purge any air. When completely full and purged check
system for leaks. The heating source (immersion heater(s) or boiler) can then be switched on.
© Baxi Heating UK Ltd 2015
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