Here's a general boiler sequence
HOT WATER DEMAND
1. Demand for DHW
2. Domestic hot water flow switch operates (continuity)
3. Control PCB sends 240Vac to the pump and the pump runs.
*** If the pump fails no fault condition is displayed, but boiler will still operate
4. The C'HTG (primary) NTC is checked to see if in range.
*** If the primary NTC is faulty then only the pump will run. Also if the DHW NTC is faulty, it
will not cause the boiler to fail.
5. Ignition PCB checks Air Pressure Switch for closed circuit(continuity) between Common and
Normally Closed
6. Ignition PCB sends 240Vac to the fan and the fan runs.
7. Air Pressure Switch operates giving continuity between Common and Normally Open.
***If no continuity the fan continues to run for 60 seconds, the Orange Flame Failure light
illuminates and the fan stops.
8. Ignition PCB energises spark generator and spark commences.
9. Simultaneously the PCB sends 240Vac to the Pilot Solenoid on the gas valve and the pilot lights.
10. Flame rectification takes place and 240Vac is sent to the main Gas Valve Solenoid, allowing
gas to the burner.
11. Main burner ignites, and the voltage at the modureg increases to give the required gas
pressure (max voltage 15Vdc, this giving full gas pressure)
***Any failure at points 7,8 and 9 will result in flame failure fault condition-
after approx 40 seconds the orange Flame Failure Light will illuminate, the appliance will
lockout and the pump will run continuously.
12. Water temperatures are maintained under the control of the DHW NTC in conjunction with the
gas valve (modureg), hot water potentiometer and the PCB.
*** If the DHW NTC fails then HW is still provided but no modulation of the gas valve takes
place and the water temperature is higher with much more boiler noise
