Viessmann Vitocal 250-A Error F.1044: High Pressure Switch Open
Safety fault F.1044 triggers when the electromechanical high-pressure switch (PSH) in the R290/R410A refrigerant circuit trips and opens the safety chain, usually exceeding approximately 28 to 31 bar due to poor secondary heat dissipation, air locks, pump failure, or overcharging.
Hardware Diagnostic Matrix
Spec Ref #ec4afeb6Required Diagnostic Tools & Instrumentation
Multimeter Probing Targets & Circuit Tolerances
Bench Calibrated ±5%| Test Point / Circuit | Target Nominal Spec | Expected State | Fault Condition |
|---|---|---|---|
| Main Logic DC Bus | 3.3V / 5.0V DC (±0.1V) | Stable DC Potential | <2.9V (Brownout / Sag) |
| Thermistor / NTC Sensor | 10kΩ - 100kΩ @ 25°C | Smooth Thermal Curve | 0Ω (Short) or ∞ (Open) |
| Safety Ground / PE Continuity | < 0.5Ω Resistance | Solid Earth Bond | > 1.0Ω (Floating Chassis) |
Common Symptoms & Fault Manifestations
- Compressor immediately halts and locks out
- Heat pump switches to auxiliary electric backup heater
- Display indicates fault message F.1044 with red warning LED illuminated
- Flow and return temperatures exhibit abnormally high differential before lockout
Root Causes & System Failure Modes
Insufficient secondary flow rate caused by a seized secondary circulation pump (PWM signal failure or mechanical blockage)
Severe airlocks in the plate heat exchanger (condenser) or fouled magnetic dirt separator / Y-strainer
All zone valves or thermostatic radiator valves (TRVs) closed without an active bypass valve
Defective high-pressure switch contact or broken wiring harness to terminal block X14/safety input on the refrigeration module (EHCU)
Refrigerant overcharge or non-condensable gases within the sealed refrigeration circuit
High-Voltage & Mechanical Safety Isolation
Prior to opening access panels, disconnecting terminals, or probing wiring, perform complete lock-out / tag-out (LOTO). Disconnect all AC mains, DC string isolators, and lithium battery banks. Allow internal smoothing capacitors at least 3 to 5 minutes to dissipate stored residual energy below safe threshold (<30VDC).
Step-by-Step Diagnostic & Resolution Procedure
Safe Isolation & Initial Inspection
Isolate the indoor and outdoor units at both main rotary isolators and lock off. Remove front casing panels. Verify absence of voltage across main terminals L1/L2/L3/N using a CAT III rated multimeter.
Hydraulic Circuit & Strainer Verification
Inspect the system primary/secondary water flow. Check system pressure (must be 1.5–2.0 bar). Clean the integrated Y-strainer and magnetic dirt separator. Open manual and automatic air vents on the condenser circuit to bleed any trapped air. Ensure the differential bypass valve is calibrated to minimum design flow (minimum 1000 L/h for Vitocal 250-A).
Secondary Circulation Pump Diagnostics
Inspect the secondary circulation pump for mechanical seizure. Restore power safely and enter actuator test mode via the ViGuide service menu. Force pump output to 100%. Check PWM signal voltage (0-10V or digital PWM) and verify line voltage at pump terminal. Replace circulation pump or capacitor if seized or failing to develop flow.
High-Pressure Switch (PSH) & Continuity Test
Locate high-pressure switch PSH in the outdoor inverter module. Unplug the connector leads and test continuity across the switch contacts using an ohmmeter (system cooled/equalized). If resistance is > 1 Ohm while system pressure is normal, replace the PSH switch. If closed (< 0.5 Ohm), inspect harness wiring back to the controller PCB for corrosion or terminal displacement.
Refrigeration Circuit & Heat Rejection Analysis
Qualified F-Gas / R290 technician: Mount temperature clamps on condenser liquid and gas lines. Run unit in heating mode. Check that condensing temperature stays within limits (typically below 58°C at nominal flow). If pressure spikes instantaneously with normal flow, reclaim and weigh refrigerant charge to verify exact factory plate rating.
Hardware Reset & Fault Clear Sequence
Controller ProcedurePrevention & Routine Maintenance Guidelines
- Ensure at least one low-resistance bypass circuit or buffer tank remains unvalved by TRVs at all times.
- Annually service and flush the magnetic dirt filter and inline strainers to maintain designated volume flow.
- Verify pre-charge pressure of expansion vessel annually to prevent hydraulic shock and rapid pressure fluctuations.
Frequently Asked Diagnostic Questions
What does error code F.1044 indicate on Viessmann Vitocal 250-A?
Safety fault F.1044 triggers when the electromechanical high-pressure switch (PSH) in the R290/R410A refrigerant circuit trips and opens the safety chain, usually exceeding approximately 28 to 31 bar due to poor secondary heat dissipation, air locks, pump failure, or overcharging. In engineering telemetry, it indicates high pressure switch open requiring circuit verification.
What are the primary triggers causing error F.1044?
Diagnostic bench telemetry isolates the following common root causes: Insufficient secondary flow rate caused by a seized secondary circulation pump (PWM signal failure or mechanical blockage); Severe airlocks in the plate heat exchanger (condenser) or fouled magnetic dirt separator / Y-strainer; All zone valves or thermostatic radiator valves (TRVs) closed without an active bypass valve; Defective high-pressure switch contact or broken wiring harness to terminal block X14/safety input on the refrigeration module (EHCU); Refrigerant overcharge or non-condensable gases within the sealed refrigeration circuit.
How do I reset and clear Viessmann error F.1044?
After addressing hydraulic flow and verifying switch continuity, navigate to the controller main screen: Access 'Menu' > 'Settings' > 'Service' (Enter technician PIN) > 'Fault Memory'. Confirm rectifications, clear active faults, and press the physical or digital 'Reset' prompt for 5 seconds to clear the safety lockout. If the error status repeats immediately after clearing, discontinue clearing and test circuit continuity.
Can I safely resolve error F.1044 without specialized shop tooling?
This fault is graded as Advanced difficulty with Critical severity. Standard diagnostics require an insulated digital multimeter and appropriate hand tools. Always observe high-voltage isolation procedures.