Remeha H.00.36 Fault Code: Causes, Fixes & Repair Costs
What does the Remeha H.00.36 fault code mean?
Fault code H.00.36 is a blocking code (H-series) on Remeha boilers, most notably the Gas 220 Ace floor-standing range. It means the boiler's control unit has either lost contact with the second (secondary) return temperature sensor entirely, or the sensor is returning a reading that falls below the acceptable operating range — both of which typically point to an open circuit or a disconnected sensor. Because this is a blocking fault rather than a lock-out, the boiler will attempt to restart automatically once the underlying problem is resolved. However, if the condition persists, it can escalate to an E-series lock-out code requiring a manual reset.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Loose or damaged wiring/connector Common
The most frequent cause. The wiring harness or connector terminals linking the second return sensor to the CU-GH control board can work loose over time due to vibration, thermal cycling, or corrosion. Even a slightly loose terminal can break the circuit and trigger an open-circuit reading.
- Failed thermistor (sensor element) Common
The NTC thermistor itself can degrade or fail internally, giving an out-of-range or infinite resistance reading. This is particularly common on older appliances or where the sensor has been exposed to repeated high temperatures or moisture ingress.
- Sensor not refitted correctly after a service Sometimes
If the boiler has recently had maintenance or a repair, the second return sensor may not have been fully reseated in its pocket or its connector may not have been clicked back in securely. This is a straightforward cause that is easy to overlook.
- Control board (CU-GH PCB) fault Rare
In rarer cases where the sensor and all its wiring check out as healthy, the fault can originate at the control board itself — either a damaged input channel or a broader PCB failure. This should only be considered after the sensor circuit has been thoroughly verified.
How to fix it
- Check whether the boiler restarts on its own DIY safe
Because H.00.36 is a blocking code, the boiler should attempt an automatic restart once the fault condition clears. Observe whether heating or hot water resumes without intervention. If it does restart but the fault returns repeatedly, there is an underlying fault that needs engineer attention.
- Do not attempt to reset the boiler more than 2–3 times DIY safe
Repeatedly forcing resets on a blocking fault will not cure it and risks escalating the code to an E-series lock-out. If the boiler does not recover on its own within a short time, move on to calling an engineer rather than cycling the reset button.
- Visually check the boiler for obvious external wiring issues DIY safe
With the boiler powered down at the isolator, you may take a brief visual look around the boiler casing for any obviously disconnected plugs or cable damage visible from the outside. Do not open the boiler casing, touch internal components, or attempt any electrical work — this is for a Gas Safe engineer only.
- Book a Gas Safe registered engineer to inspect the second return sensor circuit Gas Safe engineer
A qualified engineer will open the boiler casing, locate the second return temperature sensor and its wiring loom, and inspect all connectors and terminals for looseness, corrosion, or damage. They will also test the sensor's resistance with a multimeter — a healthy NTC thermistor produces a predictable resistance at a known temperature; an open circuit (infinite resistance) or short circuit (zero resistance) confirms a faulty sensor.
- Engineer to replace the sensor if the wiring checks out Gas Safe engineer
If the wiring and connectors are sound but the sensor reads outside specification, the engineer will fit a replacement second return temperature sensor. This is typically a straightforward job on the Gas 220 Ace and is one of the more affordable repairs associated with this fault.
- Engineer to assess the CU-GH control board if the fault persists after sensor replacement Gas Safe engineer
Should the H.00.36 code persist even with a confirmed good sensor and intact wiring, the fault may lie with the input channel on the CU-GH PCB. The engineer will advise whether the board needs replacement or whether further diagnostics are required.
Parts you may need
- Second return temperature sensor (NTC thermistor) · from £35
- Sensor wiring harness / connector · from £20
- CU-GH control board (PCB) · from £320
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£350, depending on the underlying cause.
Frequently asked questions
Will my Remeha boiler restart itself after an H.00.36 fault?
Yes — the H-series prefix means this is a blocking fault, so the boiler is designed to attempt an automatic restart once the fault condition clears. If the sensor connection is only intermittently poor, you may find the boiler recovers briefly before the fault returns. A persistent or recurring H.00.36 means the root cause has not resolved and an engineer visit is needed. Left unattended, blocking faults can escalate to an E-series lock-out, which requires a manual reset after the repair.
Can I fix the H.00.36 fault myself?
The only safe checks a homeowner can carry out are observing whether the boiler self-restarts and taking a quick visual look for any obviously disconnected external wiring before the engineer arrives. All internal work — including accessing the sensor, testing wiring continuity, and replacing any component — must be done by a Gas Safe registered engineer. The Remeha Gas 220 Ace is a commercial floor-standing appliance, and its internal electrical and gas systems must only be worked on by a competent professional.
How much does it typically cost to fix an H.00.36 fault in the UK?
For most people, the repair lands between £120 and £350 including call-out, labour, and a replacement sensor if one is needed. A wiring or connector fix that requires no new parts is usually covered within the engineer's call-out and labour charge (typically £80–£150). A replacement NTC thermistor is an inexpensive part, so sensor swaps tend to sit towards the lower end of that range. If the fault has escalated to a control board (PCB) issue, costs rise significantly — a CU-GH PCB replacement on the Gas 220 Ace can add £300–£450 to the bill, but this is an uncommon outcome.
Is H.00.36 only found on the Remeha Gas 220 Ace?
The H.00.36 code is documented in the Gas 220 Ace installation and service manual and is specifically relevant to that commercial floor-standing range. Remeha's domestic boilers (such as the Avanta and Tzerra) use a different fault code system (E0, E1, etc.) and will not display H.00.36. If you are seeing this code on a different Remeha commercial model, the underlying meaning — a fault with the secondary return temperature sensor — is likely the same, but always cross-reference your specific model's manual or ask your engineer to confirm.