Combi and system boilers use a diverted valve to switch between heating and hot water. If it's stuck in heating mode, you'll have radiators working but no hot water. If it's failed electrically, it might not move at all. We'll test it and replace it if needed. Common fault in boilers over 5 years old.
If you've got a hot water cylinder with an immersion heater (common in older Swindon properties around Railway Street and Military Road), the heating element can burn out. You'll have no hot water but the central heating still works. We'll test the element with a multimeter and replace it if it's dead.
The boiler's hot water thermostat tells it when to fire up to heat water. If it's failed, the boiler won't know you're drawing hot water and won't heat it. The heating will still work because that's a different circuit. We'll test the thermostat and replace it if faulty.
The PCB (printed circuit board) controls everything on a modern boiler. If the hot water circuit on the PCB has failed, you'll have heating but no hot water. PCBs are expensive (£200-£400 for the part alone), so if your boiler's old, it might be worth considering replacement instead.
If you've got a system boiler with a hot water cylinder, the cylinder has its own thermostat. If it's failed or set too low, you won't get hot water even though the boiler's working fine. We'll check the thermostat setting and replace it if it's faulty.