Andrews E47 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews E47 fault code mean?
The E47 fault code on Andrews boilers indicates that the boiler's primary temperature sensor (sensor 1) has reported a reading that falls outside the acceptable operating range — either unexpectedly low or dangerously high. The boiler's safety system interprets this as a potential risk and locks out, requiring a manual reset once the underlying problem has been identified and resolved. The sensor in question is typically an NTC thermistor, a small component that tracks water temperature by varying its electrical resistance. When the control board (PCB) receives a signal it cannot trust — whether due to a failed sensor, a wiring fault, or a genuine overheating event — it triggers the E47 lockout to protect the boiler and your home.
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 degraded NTC thermistor Common
The NTC temperature sensor itself has failed or drifted so far out of calibration that its resistance readings no longer match the actual water temperature. This is the most frequent cause of the E47 code. The sensor is a consumable component that can deteriorate over years of thermal cycling, particularly in hard-water areas.
- Loose or corroded wiring connections Common
The electrical connector between the NTC sensor and the PCB can work loose over time due to vibration, or corrode in the damp environment inside a boiler cabinet. Even a slightly poor connection can cause intermittent or wildly inaccurate resistance readings, triggering the lockout without the sensor itself being faulty.
- Genuine overheating due to poor water circulation Sometimes
Rather than a sensor fault, the boiler may actually be overheating. A seized or underperforming pump, a partially blocked heat exchanger, or very low system water pressure can all restrict flow to the point where the water temperature climbs beyond safe limits. In this scenario, the sensor is doing its job correctly — it really is detecting excessive heat.
- Scale or magnetite contamination affecting the sensor Sometimes
In hard-water areas, limescale can coat the sensor pocket, insulating the thermistor from the water and causing it to under-read. Similarly, a build-up of magnetite (black iron oxide sludge) can impair heat transfer and place additional thermal stress on both the sensor and the heat exchanger.
- PCB fault misreading the sensor signal Rare
In rarer cases, the control board itself develops a fault that causes it to misinterpret an otherwise healthy sensor signal. This is typically only suspected after the sensor and its wiring have been confirmed as good by an engineer testing resistance values with a multimeter.
How to fix it
- Check your system pressure DIY safe
Look at the pressure gauge on the boiler. For most Andrews boilers it should read between 1.0 and 1.5 bar when cold. If it has dropped below 1 bar, top up through the filling loop until pressure is within range. Low pressure can contribute to poor circulation and apparent temperature sensor faults.
- Attempt a single manual reset DIY safe
Press the RESET button on the boiler once and allow the boiler a full start-up attempt. If the E47 clears and the boiler runs normally, monitor it over the next hour or so. Do not press reset repeatedly — if the fault returns promptly, further resets will not resolve the underlying problem and may mask a genuine safety issue.
- Check the condensate pipe for freezing (winter months) DIY safe
Although E47 is a temperature sensor code rather than a condensate fault, a frozen condensate pipe can cause a cascade of unusual lockouts. In cold weather, check whether the plastic condensate pipe that exits the boiler to the outside or an internal drain has frozen solid. If so, carefully apply warm (not boiling) water or a hot water bottle to the pipe to thaw it, then reset the boiler.
- Do not open the boiler casing — call a Gas Safe engineer Gas Safe engineer
If the fault persists after one reset, the next steps all require access to the inside of the boiler. A Gas Safe registered engineer will remove the casing safely, locate the NTC thermistor and its wiring harness, and use a multimeter to measure the sensor's resistance across a range of temperatures and compare those readings against Andrews' specifications. This is not a homeowner task.
- Engineer to inspect and test the NTC thermistor and wiring Gas Safe engineer
The engineer will check the sensor connector for corrosion or looseness, clean or re-seat any suspect connections, and if the thermistor is out of specification, replace it with a genuine Andrews-approved part. Andrews boilers now fall under the Baxi Group, so parts can be sourced from Baxi-approved suppliers or directly through Andrews Water Heaters' service line.
- Engineer to check pump operation and heat exchanger condition Gas Safe engineer
If the sensor and wiring test as healthy, the engineer will investigate whether genuine overheating is occurring. This involves checking that the pump is running at the correct speed, that there are no blockages in the heat exchanger, and that water flow rates are within specification. A powerflush may be recommended if significant sludge or scale is found.
- Engineer to assess the PCB if all other components check out Gas Safe engineer
As a last resort, if the thermistor, wiring, pump, and heat exchanger are all confirmed to be in good condition, the engineer may suspect the PCB is at fault. PCB diagnosis and replacement must be carried out by a qualified engineer, as it involves working with the boiler's main control electronics.
Parts you may need
- NTC thermistor / temperature sensor (Andrews/Baxi compatible) · from £28
- Wiring harness / sensor connector loom · from £35
- Circulation pump (if found to be seized) · from £95
- PCB (control board) · from £220
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–£300, depending on the underlying cause.
Frequently asked questions
Can I fix the Andrews E47 fault myself by just pressing reset a few times?
A single reset is worth trying — sometimes a momentary sensor glitch or a brief overheat event will self-resolve and the boiler will run normally afterwards. However, if the E47 code returns after one reset, pressing the button repeatedly will not fix the problem and could allow an underlying issue (such as genuine overheating) to continue unchecked. At that point you need a Gas Safe registered engineer to diagnose the root cause.
How much does it cost to fix an Andrews E47 fault?
For the most common cause — a failed NTC thermistor — you can typically expect a total bill of £120 to £300 including the part (usually £15–£40) and an engineer's call-out and labour. If the fault turns out to be caused by a seized pump, the cost will be towards the higher end of that range. In rarer cases where the PCB needs replacing, costs can rise significantly beyond £300, but this is not the typical outcome and should only be considered once cheaper causes have been ruled out.
What is an NTC thermistor and why does it cause lockouts?
An NTC (Negative Temperature Coefficient) thermistor is a small electronic sensor that measures water temperature by changing its electrical resistance as it heats up or cools down. The boiler's PCB reads that resistance value continuously to know whether the water is at the right temperature. If the thermistor fails, shifts out of calibration, or loses its connection, the PCB receives a reading that is either impossibly low or dangerously high — and as a safety measure it shuts the boiler down and displays a fault code such as E47.
Is Andrews still a separate brand or is it part of another company?
Andrews Water Heaters is now part of the Baxi Heating UK Group. The Andrews brand continues to operate, particularly in the commercial and semi-commercial water heating market, but parts, service, and authorised engineer referrals are handled through the wider Baxi network. If you need a genuine replacement NTC sensor or other Andrews-approved part, contact Andrews Water Heaters' service line or a Baxi-approved heating supplier.