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HVAC Mate

HVAC Mate
Domestic Heating
HVAC Mate
Fault Finding
Ariston — Fault Finding
Common faults, codes and recommended actions. Always confirm against the appliance's own fault code sticker or manual, and follow safe isolation procedure before investigation.
101
Overheat / safety thermostat tripped
Check pump operation, system flow, and NTC sensors; reset once cause is resolved.
108
Air pressure switch fault / blocked flue or air inlet
Check flue and terminal for blockage, inspect fan and pressure switch tubing/contacts.
109
Air pressure switch stuck closed before fan starts
Check pressure switch wiring and tubing for damage; replace switch if it fails to open.
501 / 502
No ignition / loss of flame during operation
Check gas supply and inlet pressure, ignition electrode gap and condition, and earthing/polarity.
605
Flow (NTC) sensor fault
Check NTC sensor resistance against manufacturer chart and wiring continuity; replace if out of range.
203
Return sensor fault
Check return NTC sensor resistance and connector; replace if faulty.
Low pressure indicator
System water pressure low
Re-pressurise via filling loop, check for leaks and correct expansion vessel charge.
Baxi — Fault Finding
Common faults, codes and recommended actions. Always confirm against the appliance's own fault code sticker or manual, and follow safe isolation procedure before investigation.
E133
Loss of gas / ignition failure (locked out)
Check gas supply/isolation valve open, inlet pressure, and ignition electrode. Reset once corrected.
E110
Overheat thermostat / high limit tripped
Check for restricted flow, pump operation, and airlocks before resetting.
E119
Low system water pressure
Re-pressurise via filling loop and check for leaks or a failed expansion vessel.
E125
Pump stuck / circulation fault after extended run
Free/replace pump, check for debris or airlock, verify pump speed setting.
E128
Flame loss during operation
Check gas supply consistency, condensate trap/pipe for blockage, and flue terminal.
E133
Repeated ignition lockout
Verify gas rate/pressure, electrode spark gap and condensate trap is not blocked/frozen.
E168 / E169
Fan speed fault
Check fan wiring, PCB fan output, and flue restriction.
Glow-worm — Fault Finding
Common faults, codes and recommended actions. Always confirm against the appliance's own fault code sticker or manual, and follow safe isolation procedure before investigation.
F1
Low system water pressure
Re-pressurise via filling loop; check for leaks and expansion vessel charge.
F2
Flame failure / no ignition
Check gas supply, inlet pressure, and ignition electrode condition and gap.
F4
NTC flow/return sensor fault
Check sensor resistance against chart and connector condition; replace if faulty.
F9
Fan speed / air pressure fault
Check flue/terminal for blockage and fan wiring; verify pressure switch operation.
F22
Low water pressure detected during operation
Same as F1 — check for leaks before repressurising repeatedly.
F28
Failed ignition (lockout after repeated attempts)
Check gas rate/pressure, electrode, and flue condition; investigate condensate blockage.
F75
Pressure sensor fault / no pressure rise detected
Check pump operation and pressure transducer wiring/connection.
Vaillant — Fault Finding
Common faults, codes and recommended actions. Always confirm against the appliance's own fault code sticker or manual, and follow safe isolation procedure before investigation.
F.22
Low system water pressure
Re-pressurise via filling loop; check for leaks and expansion vessel charge.
F.28
Fault on ignition / no flame detected at start-up
Check gas supply and pressure, ignition electrode, and earthing/polarity.
F.29
Flame loss during operation
Check gas rate, condensate trap for blockage, and flue terminal for obstruction.
F.61
Gas valve fault
Check gas valve wiring and operation; replace valve if it fails to open/close correctly.
F.75
Pump/pressure rise not detected
Check pump for airlock or seizure, and pressure sensor wiring.
F.32
Fan speed fault
Check fan operation, wiring, and flue for restriction.
F.83
Communication fault (appliance to control/PCB)
Check control wiring/connections; reset and reflash/replace PCB if fault persists.
Worcester Bosch — Fault Finding
Common faults, codes and recommended actions. Always confirm against the appliance's own fault code sticker or manual, and follow safe isolation procedure before investigation.
EA
No ignition / flame not detected at start-up
Check gas supply and pressure, ignition electrode gap/condition, and earthing/polarity.
D5
Low system water pressure
Re-pressurise via filling loop; check for leaks and expansion vessel charge.
C6
Fan fault (speed feedback not matching demand)
Check fan wiring/connector and flue for restriction; replace fan if faulty.
F7
Flow/return temperature sensor mismatch or fault
Check sensor resistance against chart and pump operation for restricted flow.
A1
Frost protection activated / low return temperature
Usually not a fault in cold weather; check system flow and sensors if it occurs when warm.
H07
Waiting for external control / no demand signal
Check room thermostat/programmer wiring and settings.
228
Ignition lockout after repeated failed attempts
Check gas rate/pressure, electrode, and condensate trap for blockage/freezing.
Ideal — Fault Finding
Common faults, codes and recommended actions for Ideal Logic, Logic+, Logic Max, Vogue and Independent ranges. Always confirm against the appliance's own fault code sticker or manual, and follow safe isolation procedure before investigation.
F1
Low system water pressure
Re-pressurise via filling loop to approx 1.0–1.5 bar cold; check for leaks and expansion vessel charge if pressure drops repeatedly.
F2 / L2
Flame loss / ignition lockout
Check gas supply and inlet pressure, ignition electrode condition/gap, and condensate trap/pipe for blockage or freezing before resetting.
F3
Fan fault
Check fan wiring/connector, PCB fan output, and flue/terminal for restriction; replace fan if faulty.
F4 / L4
Flow thermistor fault
Check flow NTC sensor resistance against manufacturer chart and wiring continuity; replace if out of range.
F5
Return thermistor fault
Check return NTC sensor resistance and connector; replace if faulty.
F6
Outside sensor failure
Check outdoor sensor wiring and connections (weather compensation models); replace sensor if open/short circuit.
F7
Low mains voltage
Check incoming electrical supply voltage and wiring connections; investigate building supply if voltage is genuinely low.
F9 / L9
Unconfigured or faulty printed circuit board (PCB)
Check PCB configuration/DIP switches per model; reconfigure or replace PCB if fault persists.
L1
Flow temperature overheat lockout / no water flow detected
Check pump operation, system flow, airlocks and open radiator valves; verify flow sensor before resetting.
L3
No flow thermistor fault / loss of water flow
Check pump, system flow rate and blockages; check flow thermistor wiring and resistance.
L5 / LC
Boiler has reset too many times in a short period (repeated lockout cycling)
Not a fault in itself — check fault history/log to find the underlying repeating fault (commonly F1 or L2) and address the root cause.
L6
False flame detection / flame signal fault
Check flame electrode condition, earthing/polarity, and PCB flame detection circuit.
C0
Central heating demand / signal issue
Check room thermostat/programmer wiring, settings and demand signal to the boiler.
C2
Boiler chip card (BCC) fault
Check the boiler chip card is correctly fitted and configured; replace if faulty (System/Regular models).
Status 0
Boiler idle / no current demand — not a fault
Normal standby display; if it persists with no heating/hot water response, check thermostat/programmer demand and wiring.
HVAC Mate
Air Conditioning
HVAC Mate
Fault Finding
Panasonic — Fault Finding
Common faults, codes and recommended actions for Panasonic air conditioning and air source heat pump units. Codes vary between domestic split, VRF and Aquarea ranges — confirm against the indoor unit display or manual before acting.
H07
Indoor/outdoor unit not communicating correctly
Check inter-unit wiring, connections and unit addressing/pairing.
H12
Indoor/outdoor capacity mismatch
Confirm the correct outdoor unit is paired with the indoor unit(s); check DIP switch/model settings.
H14 / H23
Indoor temperature or pipe sensor fault
Check sensor resistance and connector; replace sensor if reading is open/short circuit.
H97
Outdoor fan motor fault/lock
Check fan motor wiring, obstruction, and bearing; test motor resistance.
F16
Compressor overcurrent
Check refrigerant charge, compressor winding resistance, and supply voltage.
E9
Expansion valve (drive motor) fault
Check valve coil connection and drive signal from the PCB; replace if faulty.
Low output/no heating (Aquarea)
Low refrigerant charge or restricted flow
Check for leaks, refrigerant subcooling/superheat, and water/air flow through the system.
Grant — Fault Finding
Common faults, categories and recommended actions for Grant air source heat pumps (e.g. Aerona3). Exact fault codes and numbering vary by model and firmware — always check the controller display and installation manual.
High pressure fault
System pressure switch tripped
Check for restricted water/air flow, blocked filters, and closed valves; check pressure switch wiring.
Low pressure fault
Refrigerant low pressure switch tripped
Check for refrigerant leaks, and outdoor coil for ice/blockage/airflow restriction.
Communication fault
Loss of comms between outdoor unit and controller
Check the control cable/bus wiring and connections between outdoor unit and indoor controller.
Compressor overcurrent/overload
Compressor drawing excess current or overheating
Check supply voltage, compressor winding resistance, and refrigerant charge.
Defrost fault
Outdoor coil not defrosting correctly, icing up
Check defrost sensor, reversing valve operation, and outdoor fan for obstruction.
Flow/temperature sensor fault
Water flow or temperature sensor reading out of range
Check sensor wiring and resistance against manufacturer chart; bleed air from the system.
Low system flow
Insufficient water flow through heat pump
Check pump operation, strainer/filter for debris, and system balancing valves.
Vaillant — Fault Finding (Air Source)
Common faults, categories and recommended actions for Vaillant air source heat pumps (e.g. aroTHERM). These units use a different fault numbering system to Vaillant gas boilers — always confirm the exact code against the unit's own display and manual.
Low system pressure
Heating circuit water pressure too low
Re-pressurise via filling loop; check for leaks and expansion vessel charge.
Refrigerant pressure fault
High or low refrigerant pressure switch tripped
Check outdoor unit airflow, coil condition/icing, and check for refrigerant leaks.
Sensor fault (flow/return/outdoor)
Temperature sensor reading out of range or open circuit
Check sensor resistance and wiring; replace sensor if faulty.
Communication fault
Loss of comms between outdoor unit and indoor controller
Check eBUS/control wiring and connections between indoor and outdoor units.
Compressor fault
Compressor fails to start or trips on overload
Check supply voltage, compressor windings, and refrigerant charge/pressures.
Defrost fault
Outdoor unit icing up, defrost cycle not completing
Check defrost sensor and reversing valve; check outdoor fan and coil for obstruction.
Flow fault
Insufficient water flow through the heat pump
Check circulation pump, system filter, and bleed air from the circuit.
Mitsubishi — Fault Finding
Common faults, codes and recommended actions for Mitsubishi Electric air conditioning and Ecodan air source heat pump units. Codes are broadly consistent across the range but confirm against the unit's remote controller/display.
P1
Suction/intake air thermistor fault
Check thermistor resistance and connector; replace if open/short circuit.
P4
Drain sensor fault
Check drain sensor wiring and condition; clean or replace as needed.
P5
Drain pump fault / float switch tripped
Check drain pump operation and pipework for blockage; clean float switch.
P6
Freeze/overheat protection activated
Check refrigerant charge, filter cleanliness, and airflow across coil.
U2
Power supply voltage abnormality
Check incoming supply voltage and wiring connections at the outdoor unit.
E6 / E7
Indoor/outdoor communication fault
Check inter-unit control wiring and connectors; check unit addressing on multi-systems.
E9 (Ecodan)
Outdoor unit general fault
Check outdoor unit PCB fault log, compressor, and refrigerant pressures.
Daikin — Fault Finding
Common faults, codes and recommended actions for Daikin air conditioning and air source heat pump (Altherma) units. Confirm the exact code against the unit's remote controller/display, as numbering can differ by range.
A1
Indoor unit PCB fault
Check indoor PCB connections; replace PCB if fault persists after reset.
A6
Indoor fan motor fault
Check fan motor wiring and for obstruction; test motor resistance.
E1 / E3
Outdoor PCB fault / high pressure fault
Check outdoor PCB, high pressure switch, and airflow/blockage at outdoor coil.
E4
Low pressure fault
Check for refrigerant leaks and restricted flow; check low pressure switch.
E7
Outdoor fan motor fault
Check fan motor wiring, obstruction, and bearing condition.
F3
Discharge pipe temperature too high
Check refrigerant charge, airflow, and expansion valve operation.
U4 / U2
Communication fault / power supply fault
Check inter-unit wiring and incoming power supply; check unit addressing on multi-systems.
HVAC Mate
Commercial
Plantroom Ventilation
Estimates permanent free area ventilation for a plantroom based on total net heat input and flue type, following commonly used commercial gas industry allowances (BS 6644 / IGEM guidance). Open-flued: 5.5 cm²/kW low level + 2.75 cm²/kW high level (combustion + cooling air), direct to outside air. Room sealed: a smaller cooling-only allowance, commonly around 2 cm²/kW at a single high-level opening. Always confirm against the specific appliance manufacturer's instructions and the current edition of the standard, as requirements vary by appliance type, plantroom air change rate, size and location.
Open-flued appliances need ventilation for both combustion air and cooling, using the full low/high level allowance below.
Enter a heat input greater than 0.
Where not all appliances in the plantroom can fire at the same time, ventilation can be based on the maximum probable simultaneous load rather than the full connected total. Only apply a reduced factor where this is confirmed by the system design/controls — if in doubt, use 100%.
Effective Heat Input Used for Calculation
0 kW
Low Level Free Area (air inlet)
0 cm²
High Level Free Area (air outlet)
0 cm²
1. Volume & Purge
Used for both the purge volume and the correct IGEM/UP/1B Ed. 4 tightness table (NG, LPG and LPG/Air each have different permissible drops).
Add Pipework Sections
Enter a length greater than 0.
Pipework + Meter Volume
0.0000 m³
+ Fittings Allowance (IVf, 10% of pipework)
0.0000 m³
Total Installation Volume (IV)
0.0000 m³
IGEM/UP/1B Ed. 4 Tightness Allowance
-
5. Purging
No pipework entered yet -- purging is based on the Installation Volume, so enter your meter and pipe runs there first.
Installation Volume (from the previous screen)
0.0000 m³
Fittings on Site
IGEM/UP/1B Ed. 4 accounts for fittings as a flat 10% of pipework volume, already included above. This list is for your own on-site record -- it doesn't change the calculated figures.
Required Purge Volume (PV = 1.5 × IV)
0.0000 m³
2. Tightness Testing
Existing (appliances connected)
New Installation
A new installation must show no pressure drop at all. The IV-based allowance below only applies to an existing installation with appliances connected.
Permissible Pressure Drop (IGEM/UP/1B Ed. 4)
-
0.0s
IGEM/UP/1B Ed. 4 standard duration: allow 1 minute for the pressure to stabilise, then time the test for exactly 2 minutes.
Start the timer the moment you record the start pressure, stop it the moment you record the end pressure.
Pressure Drop / Status
0.0 mbar
Test Duration
0.0s
3. Gas Flow Rate
Imperial
Metric
0.0s
Start the timer at the beginning of a dial revolution, and stop it the instant the dial completes exactly one revolution.
Time it with the stopwatch above before calculating.
Metric meters show a digital cumulative reading rather than a dial to time — take two readings a short time apart instead.
Just type the digits as shown on the meter, no decimal point needed -- the last 3 digits are treated as litres (e.g. 1234150 means 1234.150 m³).
End reading must be greater than the start reading.
Use the CV shown on the gas supplier's certificate or meter data — this defaults to a typical UK natural gas value, but always confirm against the actual site figure.
This result looks unusually high for a domestic appliance -- double check your meter readings include the decimal point in the right place (e.g. 01234.150, not just 150).
Heat Input Output
0.00 kW (GROSS)
0.00 kW (NET)
Net Reading (Volume Used)
0.000 m³
Volumetric Rate
0.00 ft³/hr
4. Heating Heat Loss
All dimensions must be greater than 0.
Required Radiator / Boiler Output
0.00 kW
Heat Output in BTU/hr
0 BTU/hr
Detailed Heat Loss Calculator
Room-by-room fabric & ventilation heat loss (simplified BS EN 12831 method). External design temp fixed at -2°C. For guidance only — confirm against full survey for accurate radiator/boiler sizing.
All dimensions must be greater than 0.
Required Radiator / Boiler Output
0.00 kW
Heat Output in BTU/hr
0 BTU/hr
Property Rooms
Property Total Heat Loss (0 rooms)
0.00 kW
Total BTU/hr
0 BTU/hr
6. AC Cooling Load
All dimensions must be greater than 0.
Required Cooling Capacity
0.00 kW
Cooling Capacity in BTU/hr
0 BTU/hr
7. Refrigerants & PT Slider
ODP Rating
0.00
GWP Rating
675
Boiling Pt @ 0 barg
-51.7 °C
Safety Class
A2L
Pressure / Temperature Calculator
Gauge bar(g)
Absolute bar(a)
bar(g)
Gauge is what a manifold set reads on site. Absolute = gauge + 1.01325 bar (atmospheric).
Bubble Point (Liquid)
0.0 °C
Subcooling Baseline
Dew Point (Vapor)
0.0 °C
Superheat Baseline
Temperature Glide Info
Near-azeotropic: Negligible temp glide.
Values are interpolated from standard refrigerant P-T reference points. For safety-critical or legal work, cross-check against the manufacturer's current P-T card.
8. Site PDF Report
Saved Calculations Log
No calculations added yet. Run a calculation and tap 'Add to Report'.