ATAG fault code C 78
Fault code C 78 on an ATAG boiler (including A203C and A244CL) means: Water pressure sensor fault. Reset the appliance once. If the code comes back, a part is usually faulty, often a temperature sensor. 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 C 78 on an ATAG boiler indicates: Water pressure sensor fault.
Fixing fault code C 78: 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.
- If it is lower, top up to 1.5–2 bar with the filling valve or filling loop, then close the valve again.
- Bleed the radiators with a radiator key, then check the pressure again and top up if needed.
- Reset the appliance once. If the code comes straight back, do not keep resetting it.
- Does the pressure drop again within a few days, or does the code come back? Then there is a leak somewhere (radiator, pipe, pressure relief valve or expansion vessel) or the pressure or flow sensor is faulty.
Applies to
ATAG A203C, A244CL, A244EC, Enigma, A203C / FGO … autom: LMUB, A244CL / FGO, A244EC / FGO … autom: LMUB, E223C / FGO … autom: LMUB, E264C / FGO … autom: LMUB, E264EC ALEC, E320S / FGO … autom: LMUB, E325C / FGO … autom: LMUB.
Click a model for the parts list and exploded view of that appliance.
Fault code C 78 on other ATAG series
The same code does not mean the same thing on every series. Check the rating plate to see which series you have:
- C 78 on A-series, E-series, A244C, A285C, A285EC, E223C: Water pressure sensor out of range or not connected or, if water pressure OK: pump defective.
Matching parts
ATAG parts are available from Instalpunt; shipping to EU countries from €12.95 (€16.95 for more distant countries), usually 3–5 working days.
Parts per Atag-series: A Series · i Series (iCon) · Q Series · E Series · P-series (iCon) · Blauwe Engel · XL-series.
Based on the cause, these original ATAG parts fit (always check the type number of your appliance):
- Atag water trap pressure sensor € 33.98
- Atag water pressure sensor Huba € 139.98
- Atag O-ring 5 x 2 mm flow sensor/flow/return 5 pcs € 24.46
Further reading on this cause
Other ATAG codes with the same cause
- 10 — Outdoor sensor fault (e.g. open, short-circuited, out of range)
- 102 — Pressure sensor defective
- 110 — Flow sensor fault (e.g. open, short-circuited, out of range)
- 112 — Return sensor fault (e.g. open, short-circuited, out of range)
- 114 — Outdoor sensor fault (e.g. open, short-circuited, out of range)
- 20 — Flow temperature sensor defective
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 ATAG boiler fault code C 78 mean?
Water pressure sensor fault.
How do I fix fault code C 78 on an ATAG 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 ATAG fault code C 78?
That depends on the exact cause. In the ATAG parts overview at Instalpunt you will find the current price and stock for each part.
Can I fix fault code C 78 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 ATAG boiler faults and codes at a glance →