Andrews E33 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews E33 fault code mean?
The E33 code on Andrews water heaters and boilers indicates that the control board has detected a problem with the NTC (Negative Temperature Coefficient) thermistor fitted to the central heating return pipe — the pipe carrying cooler water back into the appliance. The sensor has either lost its electrical connection completely (open circuit) or developed an internal short circuit. Either condition means the PCB can no longer receive reliable temperature data from the return side, so the appliance locks out to protect itself. Andrews systems share a European control architecture with other appliances in the same manufacturing group, and E33 is consistently used across that platform to flag this specific return sensor fault. Note: on a small number of other boiler platforms the E33 code can indicate a flame-detection issue rather than a sensor fault — always cross-check against your specific Andrews model's installation manual if you are unsure.
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
- Faulty or failed NTC thermistor on the return pipe Common
The NTC sensor itself has developed an internal short or open circuit, making it impossible for the PCB to read a valid resistance value. This is the most frequent root cause and is confirmed by measuring the sensor's resistance with a multimeter — a reading far outside the expected range at room temperature indicates sensor failure.
- Loose or corroded sensor wiring connections Common
The cables connecting the return sensor to the PCB can work loose over time, especially in environments with vibration or fluctuating temperatures. Corrosion at the connector pins also increases resistance in the circuit, which the board interprets as a sensor fault. Inspecting and reseating the connectors often resolves the code without any parts being replaced.
- Corrosion or damage at the sensor contact point Sometimes
Where the sensor body clips onto or inserts into the return pipework, mineral deposits, rust, or physical deformation can prevent good thermal and electrical contact. The sensor may appear intact but give erratic or out-of-range readings because of poor contact with the pipe.
- PCB fault causing a false sensor reading Rare
In a small number of cases the PCB's input circuit for the return sensor becomes damaged — for example by a voltage spike — and reports an E33 even though the sensor and wiring are both healthy. This is only confirmed after the sensor and wiring have been verified as good.
How to fix it
- Check the appliance has power and attempt a single reset DIY safe
Locate the reset button on your Andrews appliance (usually a red or clearly labelled button on the front panel). Press it once and allow the appliance up to two minutes to attempt a restart. If E33 returns immediately or after a short period, do not keep resetting — repeated resets without resolving the underlying fault can mask the problem and may cause further wear. One or two resets is the safe limit.
- Verify the gas supply is on DIY safe
Although E33 is a sensor fault rather than a gas-supply fault, it is worth confirming that the gas isolation valve serving the appliance is fully open and that other gas appliances in the property (hob, gas fire) are working normally. This rules out a wider gas-supply interruption before calling an engineer.
- Inspect the external wiring for obvious visible damage DIY safe
With the appliance switched off at the isolator, look at any wiring you can see without removing any panels. If a cable is clearly trapped, pinched, or shows visible burn marks on its outer sheath, note this and report it to the engineer. Do not attempt to open the appliance casing or touch internal wiring yourself.
- Contact a Gas Safe registered engineer to inspect the return sensor and its wiring Gas Safe engineer
An engineer will remove the appliance casing, locate the NTC thermistor on the return pipe, and check the resistance across the sensor terminals with a multimeter. They will also inspect the wiring harness and connector pins for corrosion or looseness. If the connector is simply loose it can be reseated; if the sensor resistance is out of specification the sensor will need replacing.
- Engineer to replace the CH return NTC sensor if faulty Gas Safe engineer
Replacement NTC sensors compatible with Andrews appliances are available from specialist heating-parts suppliers. The engineer will fit the correct replacement, ensure good contact with the pipework, and reconnect the wiring securely before testing.
- Engineer to check the CH flow sensor and associated wiring if the fault persists Gas Safe engineer
If replacing the return sensor does not clear E33, the fault may lie in shared wiring or — less commonly — the flow sensor circuit. The engineer will test the flow sensor resistance and inspect the full wiring loom between both sensors and the PCB.
- Engineer to assess the PCB if all sensors and wiring test satisfactory Gas Safe engineer
When the sensor and wiring are confirmed good but E33 persists, the input circuit on the PCB is the likely culprit. PCB replacement or repair should only be carried out by a qualified engineer using a part compatible with the specific Andrews model.
Parts you may need
- NTC return water temperature sensor (Andrews compatible) · from £18
- Sensor wiring harness / connector loom · from £25
- PCB (model-specific — Andrews commercial range) · from £280
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 £100–£300, depending on the underlying cause.
Frequently asked questions
Can I fix the Andrews E33 fault myself?
The only things you can safely do yourself are attempting a single reset and checking that your gas supply is on. Everything else — opening the casing, testing sensor resistance, replacing the NTC thermistor, or inspecting internal wiring — must be carried out by a Gas Safe registered engineer. Andrews appliances are often commercial or semi-commercial units carrying significant stored volumes of hot water, so internal work carries greater risk than a typical domestic boiler.
How much will it cost to repair an Andrews E33 fault?
For most people the repair involves an engineer call-out, a wiring inspection, and either reseating a connector or fitting a replacement NTC sensor. All-in, that typically comes to between £100 and £300 depending on your location and whether parts are needed. If the fault has caused damage to the PCB, the cost can rise considerably — a replacement PCB for an Andrews commercial appliance can be £250–£400 for the part alone — but PCB failure as the primary cause of E33 is uncommon.
Why does my Andrews boiler keep showing E33 after I reset it?
If E33 returns every time you reset, the underlying fault — most likely a failed NTC sensor or a corroded wiring connection — has not been resolved. The control board is detecting an out-of-range or absent signal from the return sensor on every startup attempt. Repeated resets will not fix this; you need a Gas Safe engineer to test and replace the faulty component.
Is E33 always a sensor fault on Andrews appliances?
On Andrews systems using a European-platform control board (which covers most modern Andrews models), E33 consistently refers to the return water NTC temperature sensor. However, on some other boiler brands that happen to use the same error number — such as certain Baxi or Keston models — E33 can mean a flame-detection fault instead. Always check your specific Andrews model's installation or user manual to confirm the meaning, particularly if your appliance is an older or less common variant.