H00.34 on a Baxi heat pump: TOutside Missing Outside temperature sensor was expected but not detected
Short answer
On a Baxi heat pump, H00.34 means: TOutside Missing Outside temperature sensor was expected but not detected. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the Assure Split ASHP (AWHP 4.5/6/8 MR + Assure AWHP-IDU 4-8 E)
The manual says: TOutside Missing Outside temperature sensor was expected but not detected.
Part involved: temperature sensor.
Likely causes:
- Check the wiring between the EHC–05 central unit PCB and the sensor. Check that the outdoor temperature sensor is connected to the EHC–05 PCB. Check that the sensor has been fitted properly. Check the Ohmic value of the sensor. Replace the sensor if necessary. Activate automatic detection of all the options and accessories. Reset the factory settings for the CN1 and CN2 parameters. Important This solution also resets all the other parameters.
On the HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP (R290)
The manual says: TOutdoor Missing Outdoor temperature sensor was expected but not detected.
Part involved: temperature sensor.
Likely causes:
- Wired sensor: Check the wiring between the central unit PCB and the sensor. Check that the sensor has been fitted properly. Check the Ohmic value of the sensor. Replace the sensor if necessary. Reset the values CN1 and CN2. This solution also resets all the other parameters. Radio-controlled outdoor temperature sensor: Check the wiring between the radio receiver and the central unit PCB (R-Bus line). Check that the radio gateway is supplied with power. Perform a pairing sequence. If necessary, perform a new pairing sequence and reduce the distance between the outdoor radio sensor and the radio receiver. Replace the sensor if necessary. Replace the radio receiver if necessary.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: yes - system restarts automatically when the cause disappears (may run in degraded/back-up mode meanwhile).
Manual reset: not required once cause removed.
What you can check
- Note the exact code shown on the controller and when it appeared.
- The manual's user steps allow switching the system off and on once to see if the error clears; if the code returns, contact the installer.
- If the code persists or returns, contact a heat pump engineer.
What the engineer will check
On the Assure Split ASHP (AWHP 4.5/6/8 MR + Assure AWHP-IDU 4-8 E)
- Check the wiring between the EHC–05 central unit PCB and the sensor. Check that the outdoor temperature sensor is connected to the EHC–05 PCB. Check that the sensor has been fitted properly. Check the Ohmic value of the sensor. Replace the sensor if necessary. Activate automatic detection of all the options and accessories. Reset the factory settings for the CN1 and CN2 parameters. Important This solution also resets all the other parameters.
Who to ask for: heat pump engineer (controls / sensors).
Certification: Manufacturer-trained heat pump engineer.
On the HP60 / Baxi Assure HP55 High Temperature Monobloc ASHP (R290)
- Wired sensor: Check the wiring between the central unit PCB and the sensor. Check that the sensor has been fitted properly. Check the Ohmic value of the sensor. Replace the sensor if necessary. Reset the values CN1 and CN2. This solution also resets all the other parameters. Radio-controlled outdoor temperature sensor: Check the wiring between the radio receiver and the central unit PCB (R-Bus line). Check that the radio gateway is supplied with power. Perform a pairing sequence. If necessary, perform a new pairing sequence and reduce the distance between the outdoor radio sensor and the radio receiver. Replace the sensor if necessary. Replace the radio receiver if necessary.
Who to ask for: heat pump engineer (controls / sensors).
Certification: Manufacturer-trained heat pump engineer.
What you might notice
Sources
- Installation and Service Manual - Air/water 'Split Inverter' heat pump Baxi Assure, Assure AWHP-IDU 4-8 E ↗ · 7762758 - v05 - 19082020 · page 89 · Reviewed 23 September 2026
- Installation, user and service manual - Indoor unit ASHP Control ↗ · 7887625 - v04 - 22072025 · page 126 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026