AWB fault code F.77
Fault code F.77 on an AWB boiler (including ThermoGrand) means: Flue gas valve/condensate pump fault. Reset the appliance once. If the code comes back, a part is usually faulty, often the siphon. You can check the water pressure and settings yourself; leave work on gas-carrying parts to a certified gas engineer.
After a safety alert (gas, flue gas, combustion), reset no more than once and call in a certified gas engineer. If you smell gas, call your national gas emergency number or 112 immediately.
Cause
Fault code F.77 on an AWB boiler indicates: Flue gas valve/condensate pump fault.
Fixing fault code F.77: step by step
- Read the water pressure on the display or gauge. With the system cold it should be between 1.5 and 2 bar.
- Bleed the radiators with a radiator key, then check the pressure again and top up if needed.
- When there is a heat demand, feel or listen whether the pump is running (a light vibration or hum).
- Reset the appliance once. If the code comes straight back, do not keep resetting it.
- If the pump is not running, or the code comes back, the pump is seized or faulty.
Applies to
AWB ThermoGrand, 45S, 65S.
Fault code F.77 on other AWB series
The same code does not mean the same thing on every series. Check the rating plate to see which series you have:
- F.77 on ThermoElegance, 25A/3: Combustion gas valve/condensate pump fault.
- F77 on ThermoElegance, 3 A (N NL), 35A, 4 A (N NL) A/2, 4 SOLO A (N NL), 5 A (N NL): Gas mechanism motor defective.
- F77 on ThermoMaster, CXV 30 A: Problems with gas valve. Gas valve defective. Wiring harness defective. Main PCB defective.
- F77 on ThermoMaster, CXV 35 A: Problems with gas valve Gas valve faulty. Wiring harness faulty. Main PCB faulty.
Matching parts
AWB parts are available from Instalpunt; shipping to EU countries from €12.95 (€16.95 for more distant countries), usually 3–5 working days.
Based on the cause, these original AWB parts fit (always check the type number of your appliance):
Further reading on this cause
- Read the full explanation: water under the boiler – condensate or a leak?
- All siphons and condensate drains of all brands, with part number and price
Fix it yourself or call an engineer?
Always consult the manual for your appliance and work safely. If in doubt or if the fault comes back, call in a qualified professional. A question about a part? Write to us at info@instalpunt.nl.
Frequently asked questions
What does AWB boiler fault code F.77 mean?
Flue gas valve/condensate pump fault.
How do I fix fault code F.77 on an AWB boiler?
First check the cause described above. Then restart the appliance using the reset button. If the message comes back, a part usually needs replacing or the fault needs to be repaired by a qualified professional.
Which parts do I need for AWB fault code F.77?
That depends on the exact cause. In the AWB parts overview at Instalpunt you will find the current price and stock for each part.
Can I fix fault code F.77 myself?
You can reset the appliance and check things like the water pressure or settings yourself. Work on gas-carrying parts must be left to a certified gas engineer.
All AWB boiler faults and codes at a glance →