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Boiler Fault Finder

S Plan (HW zone valve and HTG zone valve)

S plan (HW zone valve and HTG zone valve) Suspect the zone valve as being faulty if the valve does not operate after the following checks: Electrically isolate mains supply and remove fuse – always check a 3 amp fuse is fitted Remove junction box cover Ensure there is no 240V present at L and N terminals in junction box Remove metal cover from motorised valve head Turn electrical mains supply back on – be aware of 240 V!   If the motor fails to rotate with live applied to the brown wire and neutral applied to the blue wire (brown wire connects to T3 on room stat – calling, and the blue wire connects to T2 on room stat – satisfied) then the motor has failed to operate Note: When the valve stops, the valve remains fully open as long as live is applied to the brown wire – The valve closes under spring return when live is removed from the brown wire – The valve may also be faulty if: The orange wire only becomes live after the valve has fully opened (grey wire must also be live) (Orange connects to L on the pump and boiler only and grey wire connects to L terminal on time controller and L terminal on fused spur). If the boiler and pump continues to run when the cylinder stat and or room stat is satisfied when the time controller is in the OFF position. If using a 28m/m V4043H1106 zone valve on either hot water or heating circuits (S plan configuration only), the white wire is not needed and must be made electrically safe (cut back tight to black fly lead – no power will be on this wire). Sequence of operation: (2 port valve – Honeywell V4043H) There are five wires to the valve: brown (live to syncron motor), orange (switched live to supply power to pump and boiler), grey (permanent live to the micro switch), blue (neutral to syncron motor) and green/yellow (earth). When there is a call for heat (via room stat or cylinder stat), power is sent down the brown wire which starts the motor. When the valve is open, a micro switch is made via a cam and power is then sent to the boiler and pump via the orange wire (switched live). Power is constantly provided to the motor via the brown wire, keeping the valve open, as long as there is a call for heat. Once the call for heat is satisfied, power comes off the brown, causing the motor to be de-energised. A spring then returns the valve to the closed position, closing the micro switch and disconnecting power to the orange wire, switching off the hot water or heating zone respectively. Note: If using a 28m/m V4043H1106 zone valve on either hot water or heating circuits (S plan configuration only), the white wire is not needed and must be made electrically safe (cut back tight to black fly lead – no power will be on this wire). (3 port mid-position valve – Honeywell V4073A) There are five wires to the valve: white (from room thermostat calling for demand), orange (from cylinder thermostat calling for demand and switched live to supply power to pump and boiler), grey (from cylinder thermostat satisfied and H/W OFF of programmer blue (neutral to syncron motor) and green/yellow (earth). A typical S plan schematic: Programmer – Be aware of 240 V!   Always check the wiring, all the links are in place and that 240V on L and N is present on the back plate before suspecting a faulty programmer. The programmer is faulty if: If Live does not appear on HTG ON terminal when HTG only is selected (continuous or timed) Y plan and S plan (refer to diagrams) Live does not appear on HW OFF terminal when HW is off on programmer Y plan (refer to diagram) Live does not appear on HW ON terminal when HW only is selected (continuous or timed) Y plan and S plan (refer to diagrams) Note: When a single channel time switch is on and calling for a demand but the motorised valve is not moving on the lever to switch on the boiler, then try linking the C (common) and ON (calling) connections together on programmer back plate. (Always isolate electrical power supply and remove fuse prior to this). Should the zone valve motor across, then the programmer switching contacts are faulty. Should the zone valve remain the same, then further investigation is needed (syncron motor windings maybe burnt out or a seized valve spindle)….

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