Biasi ER07 Fault Code: Causes, Fixes & Repair Costs
What does the Biasi ER07 fault code mean?
The ER07 code appears on Biasi boilers when the control board detects a problem with the domestic hot water (DHW) temperature probe. The PCB continuously monitors readings from this probe to keep the boiler operating safely within its designed temperature range. When those readings fall outside acceptable limits — or stop arriving altogether — the boiler triggers a safety lockout and shuts itself down to prevent further internal damage. The fault is closely related to ER06, which covers the central heating probe; ER07 is specifically the hot water side. If your display is showing multiple error codes alongside ER07, this can point to a broader issue affecting all temperature sensing, such as a circulation problem or a faulty PCB. Note: a small number of industry sources describe ER07 as an ignition lockout, but the large majority of specialist references consistently identify it as a DHW probe fault — that is the definition used here.
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 DHW temperature probe Common
The probe itself may have developed an open circuit, short circuit, or simply degraded over time so its resistance readings are no longer accurate. The PCB sees readings outside the expected range and triggers the lockout. This is the single most common cause of ER07.
- Loose or corroded wiring and connections Common
Vibration, moisture, or age can cause the wiring between the probe and the PCB to work loose or corrode at the connector. The PCB interprets an intermittent or absent signal in the same way as a broken probe, producing the same fault code. An engineer can distinguish between probe and wiring faults using a multimeter.
- Sludge or limescale causing poor circulation Sometimes
A build-up of magnetite sludge in the pump or limescale inside the secondary heat exchanger can restrict water flow on the hot water circuit. Water then overheats in one area rather than circulating freely, causing abnormal temperature readings that confuse the probe logic and trigger ER07.
- Faulty PCB Rare
If the control board itself has developed a fault — particularly on boards that have been running for many years — it may misread or fail to read signals from otherwise healthy probes. This cause is more likely when ER07 appears alongside other unrelated codes simultaneously.
How to fix it
- Check for other visible issues first DIY safe
Before calling anyone out, note whether any other error codes are showing alongside ER07, whether you have hot water or heating at all, and whether the boiler has been making any unusual noises. This information will help an engineer diagnose the fault more quickly.
- Attempt a single boiler reset DIY safe
Locate the reset button on your Biasi boiler (usually a dedicated button or a turn-and-hold function on the control dial — check your user manual for the exact method on your model). Hold it as directed and see whether the boiler fires up normally. If it restarts but the code returns within a short time, there is an underlying fault that reset alone will not cure. Do not reset more than two or three times.
- Have a Gas Safe engineer test the DHW probe and its wiring Gas Safe engineer
An engineer will remove the boiler casing — which legally must be done by a Gas Safe registered professional — and use a multimeter to measure the resistance of the DHW temperature probe against the manufacturer's specification. They will also check every connector and length of wiring on that circuit. Loose connections can sometimes be re-secured without replacement; damaged wiring sections may be repaired rather than fully replaced.
- Replace the DHW temperature probe if defective Gas Safe engineer
If multimeter readings confirm the probe is out of specification, the engineer will fit a new compatible DHW temperature probe and clear the fault code. After replacement the boiler should be run through a full hot water demand cycle to confirm the code does not return.
- Inspect and flush the system if circulation is restricted Gas Safe engineer
Where sludge or limescale is suspected, the engineer may recommend a power flush or hot chemical flush of the system. This involves circulating cleaning agents at elevated temperature to break down deposits, followed by a full drain-down. After flushing, a central heating inhibitor should be added and a magnetic system filter fitted to prevent recurrence.
- Assess the PCB if all other components test correctly Gas Safe engineer
If the probe, wiring, and circulation all check out, the engineer will turn their attention to the PCB. A faulty board will need to be replaced. Given the cost of a Biasi PCB (typically £300–£500 for the part), the engineer may discuss whether repair or a new boiler installation represents better value, particularly for older appliances outside warranty.
- Contact a Gas Safe registered engineer if the code persists Gas Safe engineer
ER07 is not a fault that can be cleared by a homeowner beyond a reset. If the code keeps returning or if you have not yet had a professional inspection, book a Gas Safe registered engineer to carry out a full diagnosis. You can find registered engineers at the Gas Safe Register website (gassaferegister.co.uk).
Parts you may need
- Biasi DHW temperature probe / NTC sensor · from £25
- Probe wiring harness / connector · from £18
- Biasi PCB (model-specific) · from £380
- Pump (if circulation fault confirmed) · from £85
- Magnetic system filter (e.g. Fernox TF1 or Adey MagnaClean) · from £55
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 £140–£350, depending on the underlying cause.
Frequently asked questions
Can I fix the Biasi ER07 fault myself?
Not in any meaningful way, unfortunately. The only things you can safely do as a homeowner are attempt a reset (no more than two or three times) and make a note of any other codes on the display. Diagnosing or replacing the DHW temperature probe, testing the wiring, flushing the system, or touching the PCB all require the boiler casing to be removed — and working inside a gas appliance is legally restricted to Gas Safe registered engineers in the UK.
How much does it cost to fix ER07 on a Biasi boiler?
Most people with this fault end up paying between £140 and £350, which covers the engineer's call-out and labour plus a replacement DHW temperature probe or wiring repair. If the system needs a power flush to clear sludge or limescale, expect to add £300–£500 to that depending on the number of radiators. PCB replacement is a less common but more expensive outcome, typically £400–£600 all-in for a Biasi board — at that point it is worth discussing the boiler's age and whether a replacement boiler makes more financial sense.
Will resetting the boiler clear ER07 permanently?
A reset may clear the code temporarily, but if there is an underlying fault with the DHW probe, its wiring, or another component, the code will return — often within the same heating or hot water cycle. Repeatedly resetting without fixing the root cause will not resolve the fault and could mask a developing problem. If the code comes back after one or two resets, call a Gas Safe engineer.
Is ER07 covered under my Biasi warranty?
Biasi boilers typically carry a manufacturer's warranty of five to seven years depending on the model and registration. If your boiler is within that period, contact Biasi directly or the installer who fitted it before arranging an independent repair, as using an unauthorised engineer for warranty work can sometimes affect your cover. If you are outside the warranty period, any Gas Safe registered engineer can carry out the repair.