The flashcards below were created by user
on FreezingBlue Flashcards.
Central heating is ok, but DHW is not.
The fault can only be at:
- The diverter valve,
- flow switch,
- dhw thermostats/thermistors,
- dhw heat exchanger,
- water governor,
No dhw, diverter valve diaphragm pass type.
No dhw, diverter valve Venturi type.
- Split diaphragm.
- obstruction in Venturi ie scale, rust etc.
No dhw or dhw not at temperature and CH circuit warms. Diverter valve.
- Wax capsule lost calibration.
- capsule scaled.
No dhw or dhw not at temperature and CH circuit warms. Spindle does not move.
- Pump failing/failed.
- venturi pipe work blocked.
- filter/strainer blocked.
- diaphragm perished/split.
No dhw or dhw not at temperature and CH circuit warms. Slow movement of spindle.
- Pump failing.
- spindle shaft scaled due to leak.
- venturi partially blocked due to rust or sediment.
- water flow slow due to sealed domestic heat exchanger.
- mains pressure low.
- pressure loss at spindle sealing unit.
- air may be trapped in valve after repair.
No dhw or dhw not at temperature and CH circuit warms. Spindle moving but no response.
- Not enough spindle force due to faulty diaphragm causing pressure loss.
- not enough spindle force due to sealing unit leaking.
- microswitch faulty.
- PCB not sequencing, fan not working, ignition sequence (sparking) or faulty gas valve etc.
No HW, CH ok.
- Thermistor connections/terminals are dirty/loose.
- flow switch stuck in off position or faulty.
- thermistor open circuit/infinity caused by water ingress.
- thermistor lost calibration.
- thermostat contact points worn/burnt out/pitted.
- thermocouple phial out of position.
DHW not at temperature.
- Sludge/scale build up in main heat exchanger often causing noise - kettling.
- sludge/scale or detritous in dhw heat exchanger or thermostat.
- incorrectly sized gas pipe.
- water temperature potentiometer set too high.
Hot water alternating hot and cold.
Sludge/scale build up in domestic hot water heat exchanger.
Reduced dhw flow rate.
- Filter/strainer partially blocked by detritus.
- cartridge partially blocked by detritus.
- temporay low mains supply pressure.