Boiler Fault Finder

Solenoids & Moduregs

Solenoids Reasons a solenoid will fail to operate: Burnt out coil Poor terminal connection Loose mountings Armature sticking (Foreign matter accumulation jamming the armature) Faulty printed circuit board These electromagnetic devices are utilised to control the on/off/flow of gas through modureg gas valves. These are energised by either AC or DC current (often colour coded to indicate 24V blue and 230V black or red). As voltage is applied to the coil, the armature is drawn into the solenoid valve body, allowing gas to flow through the main gas valve which is proportional to the current applied. The modulation (varying current) increases or decreases gas flow/rate to match the heat load placed on the boiler. The temperature of the thermistor indirectly controls the amount of current the potentiometer sends to the solenoid. Typically, the pilot solenoid and main solenoids are 230V AC and the modulating solenoid approx. 24V DC, but manufacturer instructions/data must always be checked. To test a solenoid: Electrically isolate boiler / system controls Inspect terminal connections Ascertain correct solenoid voltage (manufacturer instructions) Turn on power supply to boiler 240 V LIVE TEST   Set multimeter to correct voltage scale and check at connections (AC or DC) Incorrect reading maybe faulty printed circuit board – needs further investigating Correct voltage but not operating – electrically isolate boiler Set multimeter to Ohms scale and measure coil resistance: No resistance/infinity = faulty Less than 1 Ohm = faulty Modureg coil resistance 45 +Ohms approx* = ok. *(This will vary depending on manufacturer and type of solenoid. Some modern two stage safety solenoids may be 165 + ohms) Modureg adjustments (early production boilers): Maximum adjustment: Electrically isolate supply Remove the modulator solenoid coil by releasing the spring clip and pull away from the brass spindle Turn the small black minimum rate adjusting screw fully clockwise Loosen the locking nut which secures the spindle to the gas valve Turn on power supply to boiler Call for a demand via fully opening a hot tap Rotate the brass spindle clockwise to increase the pressure to maximum setting (if needed) Tighten locking nut Minimum adjustment: With the burner still running at maximum setting Slowly unscrew the small black minimum rate adjusting screw at the end of the spindle until the correct pressure is attained Electrically isolate supply Refit the modulator solenoid coil with spring clip onto brass spindle Turn on power supply to boiler Modureg adjustments (later production models): On moduregs where the minimum and maximum adjustment nuts are enclosed behind a plastic cover, always check with manufacturer instructions first before making any adjustments. For most boilers, the large nut is for maximum pressure and the small nut is for minimum pressure, however, there are some boilers which are arranged opposite to this (large nut is minimum and small nut is maximum). In order to adjust the maximum pressure, call for a demand via fully opening a hot tap and turn the large nut clockwise to increase whilst at the same time, holding the minimum screw still. In order to adjust minimum pressure, remove one of the wires from the modureg coil terminals (this automatically drops the pressure down to low rate) and turn the small screw clockwise to increase (the large nut will not freely move so no need to hold during this adjustment). On modern gas/air ratio valves, the manufacturer’s instructions must always be followed when adjusting them. In order to achieve the correct CO / CO2 ratio at time of service or periodic inspection, the appliance must be forced into “service mode” where the gas adjustments are then made via the offset adjuster (minimum rate) and throttle adjuster (maximum rate). Note: Whenever a gas valve of this type is replaced or adjusted, a calibrated electronic combustion gas analyser MUST be used to ensure correct operation. Finally, an inlet pressure check at the gas valve, working pressure at the metre and a tightness test should be carried out on completion of commissioning….

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