Warmflow E06 Fault Code: Causes, Fixes & Repair Costs
What does the Warmflow E06 fault code mean?
The E06 code on a Warmflow boiler indicates a fault with the Domestic Hot Water (DHW) Flow NTC Temperature Sensor. This small thermistor monitors the temperature of water flowing through the hot water circuit and feeds that reading back to the boiler's control board. Because its resistance changes predictably as temperature rises or falls, the PCB relies on it to regulate DHW delivery safely. When the boiler detects a short circuit in the sensor circuit, an open circuit (disconnected sensor), or a reading that falls outside the expected range, it locks out and displays E06. Without a trustworthy signal from this sensor, the boiler cannot safely heat domestic hot water, so it shuts down as a precaution.
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
- Short circuit or open circuit in the DHW NTC sensor Common
The most direct trigger for E06. If the sensor's internal element fails — either shorting internally or breaking the circuit entirely — the PCB immediately sees an impossible reading and locks the boiler out. This is the fault Warmflow's own documentation specifically describes for E06.
- Loose or corroded wiring connector Common
The sensor connects to the PCB via a plug-in connector. Vibration, damp, or age can cause the connector to work loose or develop corrosion on the terminals. This creates an intermittent or absent signal that the boiler interprets as a sensor fault. Sometimes reseating the connector resolves the issue without replacing the sensor itself.
- Physical damage to the sensor probe or cable Sometimes
The sensor probe sits in contact with the water circuit, and its wiring runs through a warm, sometimes damp environment. Cable chafing, a kinked probe, or impact damage can break the circuit. This is more common in older boilers or those that have had previous work carried out nearby.
- Limescale or corrosion on the sensor Sometimes
In hard-water areas, limescale can build up around the sensor body, acting as insulation and causing the sensor to report temperatures that don't match actual water conditions. Over time this can push the reading outside the PCB's acceptable window, triggering E06.
- PCB fault Rare
If the sensor and its wiring test within the correct resistance range but E06 persists, the PCB itself may have developed a fault on the input channel that reads the DHW NTC. This is relatively rare and is usually confirmed only after the sensor and wiring have been ruled out.
How to fix it
- Check the boiler's gas or oil supply is active DIY safe
Before investigating the boiler itself, confirm that your gas meter isolation valve is open and that other gas appliances in the home are working normally. For oil-fired Warmflow boilers, check there is adequate fuel in the tank and that the oil supply valve is open. A supply interruption can occasionally trigger sensor-related lockouts.
- Reset the boiler once or twice DIY safe
Press and hold the reset button (refer to your model's user guide for the exact location — usually a button or a rotary control held for 3–5 seconds). If E06 clears and the boiler runs normally, monitor it over the next day. If the code returns after one or two resets, do not continue resetting — a recurring E06 points to a genuine hardware fault that needs investigation.
- Do not attempt to inspect or touch the sensor or wiring yourself Gas Safe engineer
The DHW NTC sensor is an internal boiler component connected to the PCB. Accessing it involves removing the boiler casing and working inside the appliance. On gas boilers this must be carried out by a Gas Safe registered engineer; on oil-fired Warmflow boilers it must be an OFTEC-registered engineer. Attempting this yourself would void any remaining warranty and could be dangerous.
- Arrange for a qualified engineer to inspect the sensor and its wiring Gas Safe engineer
A Gas Safe or OFTEC engineer will remove the boiler casing, locate the DHW flow NTC sensor, and use a multimeter to measure its resistance at a known temperature. A healthy NTC thermistor should show a resistance value consistent with the manufacturer's specification — any reading that is open-circuit, short-circuit, or wildly out of range confirms sensor failure. The engineer will also check the wiring harness and connector for corrosion, damage, or poor contact.
- Have the faulty sensor or wiring replaced Gas Safe engineer
The DHW NTC sensor itself is a low-cost part — typically £5–£30 depending on the Warmflow model. The engineer will fit a new sensor, reconnect the wiring, and clear the fault code before running the boiler through a full hot-water cycle to confirm the repair. The total job is usually completed within an hour.
- If E06 persists after sensor replacement, have the PCB investigated Gas Safe engineer
In a small number of cases the sensor tests as healthy but the fault code remains. This points to the PCB's NTC input circuit having developed a fault. The engineer will confirm this by testing the sensor resistance at the PCB terminals. PCB replacement is a more involved and costly repair, so a competent engineer will also check the heat exchanger, pump, and gas valve for secondary issues before confirming a PCB diagnosis.
- Call a Gas Safe registered engineer (or OFTEC engineer for oil models) if you have not already done so Gas Safe engineer
If the boiler has not responded to a reset, contact a Gas Safe registered engineer for gas-fired Warmflow boilers, or an OFTEC-registered technician for oil models. Do not attempt further resets or disassembly. Provide the engineer with the fault code (E06) so they can bring appropriate diagnostic equipment and the correct sensor part where possible.
Parts you may need
- DHW Flow NTC Temperature Sensor · from £18
- NTC Sensor Wiring Harness / Connector · from £15
- Warmflow 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 £100–£220, depending on the underlying cause.
Frequently asked questions
Can I fix a Warmflow E06 fault myself?
Not the root cause, no. The only homeowner-safe steps are checking your fuel supply is on and attempting one or two resets. The DHW NTC sensor is inside the boiler casing, and accessing or replacing it requires removing panels and working with internal wiring — work that must be done by a Gas Safe registered engineer (or OFTEC-registered engineer for oil boilers). Attempting it yourself would also invalidate any remaining Warmflow warranty, which covers defective parts for 24 months from manufacture.
How much does it cost to fix a Warmflow E06 fault?
For the most common cause — a failed DHW NTC sensor — you should expect to pay roughly £100–£220 all-in, covering the engineer's call-out, labour (the job usually takes under an hour), and the part itself (typically £5–£30). If the fault turns out to involve the PCB rather than the sensor, costs rise considerably; PCB replacement on a Warmflow boiler can run to £350–£500 or more including labour, though this is relatively uncommon for an E06 code.
Why does E06 keep coming back after I reset the boiler?
A recurring E06 strongly suggests a genuine hardware fault rather than a one-off electronic glitch. The most likely culprits are a failing DHW NTC sensor, a loose or corroded wiring connector, or — less commonly — a PCB issue. Repeated resets will not cure any of these problems and can mask the underlying fault. Book an engineer to carry out a proper diagnosis.
Is my Warmflow boiler still under warranty for an E06 fault?
Warmflow offers a 24-month warranty against defective parts and workmanship from the date of manufacture, with a 5-year warranty on the water jacket and thermal store in combi models. If your boiler is within this period, contact Warmflow or your installer before booking an independent engineer — a valid warranty claim could mean the sensor replacement is covered at no cost to you. Keep your installation documentation and commissioning certificate to hand when you call.