- Boilers
- Gas boiler
E178
Baxi E178 on a gas boiler: overheat on low temperature system
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
Baxi E178 means the overheat safety thermostat for a low temperature system, such as underfloor heating, has tripped. It is not a reset code: note when it appears and call the authorised service centre.
Safety first
Stop and check this first
- If you smell gas: Baxi says to switch the boiler off, not to operate any electrical device or switch on lights, to put out any flame and open the windows. Then leave the home and call your gas distributor's emergency number and the service centre from outside.
- If you have to top up the system often, Baxi says to contact the authorised service centre: there may be a water leak. Do not open the boiler or touch the pump.
Safe checks you can perform
- Smell of gas or combustion fumes
- What Baxi says to do for 178
- Pressure gauge with the system cold
- Pump, circulation and wiring checked by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Pump power wiring
- Do not attempt this professional task: Pump operation
- Do not attempt this professional task: Circulation in the low temperature circuit
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Pump power wiring
What they doThe technician checks the cable and connectors that feed the pump from the board.
They must show youthe connector or cable section checked.
In writingthe repair carried out.
Pump operation
What they doThe technician checks that the pump starts and moves water when the boiler calls for it.
They must show youthe pump running after the check.
In writingthe pump condition and, if replaced, its part number and why.
Circulation in the low temperature circuit
What they doThe technician checks that water flows through the low temperature system, with no closed or blocked sections.
They must show youwhere the circulation problem was, if there was one.
In writingwhat was corrected in the system.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Smell of gas or combustion fumes
- Who:
- you.
- How:
- first, check whether there is a smell of gas or combustion fumes near the boiler, or whether anyone has a headache, dizziness or nausea.
- Result that matters:
- whether it is safe to carry on with the checks for 178.
- If you smell gas:
- do not touch the boiler; follow the gas warning and call from outside.
- If you smell fumes:
- switch the boiler off, open doors and windows and call the service centre, as Baxi says.
- Evidence to keep:
- a note of the time and what you noticed.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457
What Baxi says to do for 178
- Who:
- you.
- How:
- in the user table, 178 has no reset: Baxi says to call the authorised service centre. Do not press reset again and again or cut the power to test it.
- Result that matters:
- not wasting time on resets that do not apply to this code.
- If the code stays on the display:
- note the date and time and call the service centre.
- If it clears by itself:
- note it anyway; if it repeats, Baxi says to contact the service centre.
- Evidence to keep:
- photo of the display with the code and the time.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457
Pressure gauge with the system cold
- Who:
- you.
- How:
- with the system cold, read the boiler pressure gauge. Baxi says it should be between 1 and 1.5 bar and explains how to top up with the filling tap, without tools, closing it afterwards.
- Result that matters:
- the actual system pressure.
- If it is below 1 bar:
- top up as Baxi describes; if it drops often, Baxi says to call the service centre.
- If it is fine:
- the cause lies in the pump, the circulation or the pump wiring.
- Evidence to keep:
- photo of the gauge with the date.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457
Pump, circulation and wiring checked by the technician
- Who:
- Baxi authorised service centre.
- How:
- checks the pump operation, the water circulation in the low temperature circuit and the pump power wiring.
- Result that matters:
- which of the three causes the check confirms.
- If the pump gets no power:
- the wiring is repaired.
- If the pump runs and water does not circulate:
- the low temperature circuit is checked.
- Evidence to keep:
- job sheet with what was checked and corrected.
Baxi says to disconnect the power before any work and only qualified technicians may work on the appliance. Sensors, internal wiring and the board are technician only.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457 · Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de instalación, montaje y funcionamiento para el instalador 7731458
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Baxi
- Product type
- Gas boiler
Known code variants
- 178
- Baxi 178
- Baxi E 178
- Error 178 Baxi
- Neodens Plus 178
What it means
On the Neodens Plus ECO, code 178 is activation of the overheat safety thermostat on a low temperature system, the kind used for underfloor heating. The thermostat cuts out when the water going to that circuit gets too hot. For 178, Baxi tells the technician to check that the pump works, that water circulates through the low temperature system, and the pump power wiring. The code does not say which of the three is at fault.
Warnings and stop conditions
- Criticaleditorial warning
If you smell gas: Baxi says to switch the boiler off, not to operate any electrical device or switch on lights, to put out any flame and open the windows. Then leave the home and call your gas distributor's emergency number and the service centre from outside.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457
- Mediumsource verified
If you have to top up the system often, Baxi says to contact the authorised service centre: there may be a water leak. Do not open the boiler or touch the pump.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de funcionamiento y mantenimiento para el usuario 7731457
Symptoms and causes
Probable causes · in order
- Pump not working properlyPossible
Baxi says to check that the pump works correctly. If it does not move the water, the heat stays in the boiler and the water overheats.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de instalación, montaje y funcionamiento para el instalador 7731458
- Poor circulation in the low temperature circuitPossible
With the pump fine, water may still not flow through the underfloor circuit. Baxi says to check that circulation in the system.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de instalación, montaje y funcionamiento para el instalador 7731458
- Pump power wiringPossible
Baxi says to check this wiring. A damaged cable or connector leaves the pump without power even when the pump itself is sound.
Evidence: Baxi Neodens Plus 24/24 F ECO, 28/28 F ECO y 33/33 F ECO, instrucciones de instalación, montaje y funcionamiento para el instalador 7731458
Virtual technician
Does E178 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
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