- Heat pumps
- Air-to-water heat pump
E20
Viessmann E20 on a Vitocal heat pump: discharge overtemperature
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
E20 on the Viessmann Vitocal 100-AW is the discharge overtemperature protection of the outdoor unit. Low refrigerant, scale in the heat exchanger, ice or dirt on the coil or very hot water can cause it. Lower any high setpoints and call an F-gas certified technician.
Safety first
Stop and check this first
- The Vitocal circuit contains flammable R32: if you hear hissing or suspect an escape, ventilate, move any flame, heat source or battery device away and wait for the technician without opening the casing.
- Even after you switch off the power, parts of the circuit boards stay live for a few minutes and there may be several supply circuits; leave any electrical work on the unit to a qualified installer.
Safe checks you can perform
- Confirm the message and count repeats
- Lower very high water setpoints
- Watch the frost from a distance
- Keep air circulation free
Leave these tasks to a qualified professional
- Do not attempt this professional task: Measure pressure and locate leaks
- Do not attempt this professional task: Rule out heat exchanger, defrost and valve
- Do not attempt this professional task: Verify the water sensor and filter
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.
Measure pressure and locate leaks
What they doAn F-gas certified technician reads the standstill pressure and uses a detector to find escapes; if charge is missing, they repair, evacuate and recharge the amount on the nameplate.
They must show youthe pressure reading and the leak detector result.
In writingthe repaired point and the kilograms of R32 charged.
Rule out heat exchanger, defrost and valve
What they doIf the charge is correct, they check the plate heat exchanger for scale, the defrost operation and settings, airflow through the fins and the electronic expansion valve with its coil.
They must show youat which step the anomaly appeared.
In writingeach item cleaned, adjusted or replaced during the visit.
Verify the water sensor and filter
What they doThey compare the sensor temperature with the real one and replace, insulate or relocate the sensor if needed; as a last step they recover the refrigerant and inspect the circuit filter.
They must show youthe gap between the sensor reading and the real measurement.
In writingwhether the sensor was moved or the filter changed.
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.
Confirm the message and count repeats
Read the type of message on the controller, confirm it and note the date, time and whether E40 follows. That second code shows the protection has tripped several times and the outdoor unit needs a manual reset, which the authorised service should carry out.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
Lower very high water setpoints
The troubleshooting guide in the manual lets the user temporarily reduce the normal hot water temperature and review the heating curve. If your setpoints are very high, bring them down to a sensible value and see whether E20 stops in the following days.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
Watch the frost from a distance
On cold, damp days, check without getting close whether the outdoor unit coil stays white with frost for a long time. Do not pour water or scrape the ice; take a timed photo so the technician can judge the defrost.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
Keep air circulation free
Make sure no furniture, tarpaulins or plants now enclose the outdoor unit; the manual asks for a spot with good air circulation and no corners where discharged air is drawn back in. Remove loose items only, without opening panels.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
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
- Heat pumps
- Brand
- Viessmann
- Product type
- Air-to-water heat pump
Known code variants
- 20
- AEG E20 error
- AEG Fehler E20
- AEG lavadora C2
- AEG lavadora E20
- AEG lavadora E21
- AEG lavatrice C2
- AEG lavatrice E20
- AEG lavatrice E21
- AEG lave-linge C2
- AEG lave-linge E20
- AEG lave-linge E21
- AEG Waschmaschine C2
- AEG Waschmaschine E20
- AEG Waschmaschine E21
- AEG washer C2
- AEG washer E20
- AEG washer E21
- aerotermia Viessmann E20
- Baxi 20
- Baxi E 20
- Bosch dishwasher E20
- Bosch E20
- Bosch E20 error
- C2
- code erreur AEG E20
- E20
- E20 AEG lavadora
- E20 AEG lavatrice
- E20 AEG lave-linge
- E20 AEG Waschmaschine
- E20 AEG washer
- E20 Bosch dishwasher
- E20 lavavajillas Bosch
- E21
- E22
- E23
- E24
- E:20
- Electrolux dryer E20
- Electrolux dryer E20 drain
- Electrolux E20 error tumble dryer
- Electrolux E20 lavadora
- Electrolux E20 secadora
- Electrolux washer 2 beeps
- Electrolux washer error E20
- Electrolux washer not draining
- Electrolux washing machine E20
- Error 20 Baxi
- error AEG E20
- error E20 Bosch
- error E20 lavadora Electrolux
- error E20 lavadora Zanussi
- error E20 secadora Electrolux
- error E20 secadora Zanussi
- errore AEG E20
- lavadora Electrolux 2 pitidos
- lavadora Electrolux no desagua
- lavadora Zanussi E20 no desagua
- lavavajillas Bosch E20
- Neodens Plus 20
- secadora Electrolux E20 desagüe
- secadora Zanussi 2 pitidos
- Viessmann E20
- Viessmann Vitocal 100-AW E20
- Vitocal 100-AW AM2V E20
- Vitocal E20
- Vitocal exhaust temperature overprotection
- Vitocal temperatura descarga E20
- Zanussi dryer 2 beeps
- Zanussi dryer C2
- Zanussi dryer E20
- Zanussi E20 error washer
- Zanussi E20 lavadora
- Zanussi secadora C2
- Zanussi secadora E20
- Zanussi tumble dryer error E20
- Zanussi washer E20 not draining
- Zanussi washing machine E20
What it means
The Vitocal 100-AW AM2V (Viessmann manual 6221389-11 for North America, in English) lists E20 in its outdoor unit fault table as Exhaust temperature overprotection: the gas leaving the compressor is too hot. Viessmann names seven causes: lack of refrigerant, scaling in the plate heat exchanger, heavy frost on the fins, dirty or poorly ventilated fins, abnormal throttling, high outlet water temperature and a system blockage. The same table shows E40 when discharge overheat protection trips three times, with a manual reset of the outdoor unit. E20 does not prove a leak on its own.
Warnings and stop conditions
- Highsource verified
The Vitocal circuit contains flammable R32: if you hear hissing or suspect an escape, ventilate, move any flame, heat source or battery device away and wait for the technician without opening the casing.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
- Mediumsource verified
Even after you switch off the power, parts of the circuit boards stay live for a few minutes and there may be several supply circuits; leave any electrical work on the unit to a qualified installer.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
Symptoms and causes
Probable causes · in order
- Low refrigerant chargeCommon
With too little charge the compressor overheats the gas; the technician reads the standstill pressure and hunts for the leak point before repairing, evacuating and recharging.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
- Scaling on the water sidePossible
Scale at the inlet, outlet or inside of the plate heat exchanger reduces the heat passed to the water; the manual says to restart heating only after descaling.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
- Iced or clogged outdoor coilPossible
A heavy frost layer or dirty fins that block the air disturb the cycle; Viessmann proposes a manual defrost, adjusted defrost settings and fin cleaning by a professional.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
- Expansion valve or blocked filterPossible
A stuck electronic expansion valve or one with a loose coil, or a circuit filter clogged with dirt, throttles the refrigerant flow and raises the discharge temperature.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
- High water temperature or misplaced sensorPossible
If the water leaves very hot or the sensor reads well below the real value, the manual asks to replace or move the sensor, improve its thermal contact or lower the water setpoint.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
Virtual technician
Does E20 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
- 1
Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
Viessmann · 2026 · manual
Was this entry useful?