- Heat pumps
- Air-to-water heat pump
E18
Viessmann E18 on a Vitocal 100-AW heat pump: water flow protection
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
On the Vitocal 100-AW AM2V, E18 is the outdoor unit water flow protection. Read and confirm the notification on the display, check that visible valves are open and, if it repeats, call an authorised service centre.
Safety first
Stop and check this first
- The Vitocal 100-AW outdoor unit contains flammable R32 refrigerant. Viessmann warns that some PCB components stay live after the power is switched off and requires waiting at least 4 minutes before removing covers. Do not open the unit: installation and service are for a licensed professional.
Safe checks you can perform
- Notification on the display
- Visible valves open
- Pump, venting, filter and flow switch
Leave these tasks to a qualified professional
- Do not attempt this professional task: Follow Viessmann's list before replacing parts
- Do not attempt this professional task: Secondary pump only with a calculation
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.
Follow Viessmann's list before replacing parts
What they doThe technician checks pump, air, circuit resistance, valves, filter and switch in that order.
They must show youthe clean filter, the venting done and the switch reading with a multimeter.
In writingthe confirmed cause and what was done.
Secondary pump only with a calculation
What they doIf they propose adding a secondary pump, the technician calculates the circuit's hydraulic resistance.
They must show youthe circuit resistance calculation.
In writingthe result of the calculation and the test without E18 after the work.
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.
Notification on the display
- Who:
- you.
- How:
- read the type of notification on the display and confirm it, as Viessmann describes for warning and fault messages.
- Result that matters:
- whether the notification returns after confirming it and matches outdoor unit code E18.
- If it does not return:
- note the date and watch.
- If it returns:
- call an authorised service centre.
- Evidence to keep:
- a photo of the display with the date.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
Visible valves open
- Who:
- you, without opening the unit.
- How:
- check that the visible valves on the heating circuit are open.
- Result that matters:
- Viessmann includes valves not opened among the causes of E18.
- If one was closed:
- open it and note whether E18 returns.
- If all were open:
- visible valves are ruled out; the technician checks the rest.
- Evidence to keep:
- a note of the valve found.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
Pump, venting, filter and flow switch
- Who:
- a licensed professional.
- How:
- they check that the pump runs and its indicator, vent from the high point, clean the filter, calculate circuit resistance and measure the flow switch with a multimeter.
- Result that matters:
- which cause on Viessmann's list is confirmed.
- If air comes out or the filter was dirty:
- a hydraulic cause is confirmed.
- If pump and circuit are fine and the switch does not switch:
- the switch is confirmed.
- Evidence to keep:
- a job sheet with what was checked at each point.
PCBs stay live even after power off: Viessmann requires waiting at least 4 minutes before removing covers. Licensed professional only.
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
- Balay dishwasher E18
- Balay E18
- Balay E18 error washer
- Balay E18 lavadora
- Balay washer E18 not draining
- Balay washing machine E18
- Bosch dishwasher E18
- Bosch E18
- Bosch E18 error
- Bosch E18 lavavajillas
- Bosch Geschirrspüler Fehler E18
- code erreur E18 lave-vaisselle Bosch
- code erreur E18 lave-vaisselle Siemens
- codice E18 Bosch
- codice E18 Siemens
- código E18 Bosch
- código E18 Siemens
- E 18
- E18 Bosch dishwasher
- E18 lavavajillas Balay
- E18 Siemens dishwasher
- E:18
- erreur E18 Bosch
- erreur E18 Siemens
- Error E18 Balay
- error E18 lavadora Balay
- error E18 lavavajillas Bosch
- error E18 lavavajillas Siemens
- errore E18 lavastoviglie Bosch
- errore E18 lavastoviglie Siemens
- F18
- F:18
- Fehlercode E18 Bosch
- lavadora Balay E18 no desagua
- Siemens dishwasher E18
- Siemens E00-18
- Siemens E18
- Siemens F18
- Viessmann heat pump E18
- Viessmann Vitocal 100-AW E18
- Vitocal E18
What it means
Viessmann defines E18 as outdoor unit water flow protection on the Vitocal 100-AW AM2V, a North American model. It lists six causes: water pump failure, air in the circuit, excessive circuit resistance, valves not fully open, a dirty circuit filter and a water flow switch wrongly connected or damaged. For each it gives a check: the pump indicator, the high point vent, a resistance calculation, the valves, the filter and the switch measured with a multimeter. The code does not say which.
Warnings and stop conditions
- Highsource verified
The Vitocal 100-AW outdoor unit contains flammable R32 refrigerant. Viessmann warns that some PCB components stay live after the power is switched off and requires waiting at least 4 minutes before removing covers. Do not open the unit: installation and service are for a licensed professional.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
Symptoms and causes
Probable causes · in order
- Air in the circuitCommon
Viessmann says to open the high point vent and see whether gas comes out intermittently. It fits after filling or after work on the system.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
- Closed valves or dirty filterCommon
Valves that should be open and a filter full of impurities cut flow. They are direct checks from Viessmann's list.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
- Faulty pump or excessive resistancePossible
If the pump does not run or the circuit has more resistance than it can overcome, Viessmann proposes servicing or replacing the pump or adding a secondary pump.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
- Water flow switchPossible
A loose connection or damaged switch gives E18 with correct flow. It is checked with a multimeter.
Evidence: Viessmann Vitocal 100-AW AM2V installation, service and operating instructions 6221389-11
Virtual technician
Does E18 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
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