Buderus 2F 277 Fault Code: Causes, Fixes & Repair Costs
What does the Buderus 2F 277 fault code mean?
The 2F / 277 fault is a locking fault, meaning the boiler has shut itself down and will only restart after a manual reset. It indicates that the boiler's control unit has detected either an unacceptably large temperature difference between the flow (supply) sensor and the safety sensor, or it has confirmed no measurable heat rise after the burner attempted to fire. In either case, the boiler cannot verify that heat is being generated and distributed safely, so it locks out to protect the system. The display will show the fault code alongside a flashing 'H' symbol. This fault sits within a broader family of 2F sensor and heat-rise codes. The related subcodes 271 and 274 share the same diagnostic territory: subcode 271 typically points specifically to an excessive temperature differential between the safety and supply sensors or a complete failure to achieve heat rise; subcode 274 is also associated with sensor mismatch conditions within the same fault category. Whether your display shows 2F 271, 2F 274, or 2F 277, the diagnostic approach is essentially the same — start with the sensors, then the pump, then system circulation.
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 flow or safety temperature sensor (NTC) Common
The most frequently identified root cause. The flow sensor sits on the pipe leaving the boiler and the safety sensor is mounted on the cast aluminium block. If either sensor has drifted out of range, failed electrically, or developed a poor connection, the control unit sees an implausible temperature reading and locks out. Real-world cases have been resolved simply by replacing the faulty sensor.
- Failed or seized circulation pump Common
If the primary pump is not spinning up properly on startup, water is not moving through the heat exchanger. The flow sensor sees little or no temperature rise even though the burner is firing, triggering the fault. This is often found after sensors have already been ruled out as the cause.
- Air in the system (airlock) Sometimes
An airlock prevents adequate water circulation, causing localised overheating at the heat exchanger and erratic sensor readings. This fault has been seen on initial start-up of newly installed or recently drained systems where air purging was incomplete.
- Restricted water flow or pipework bottleneck Sometimes
Undersized pipework, closed valves, or zone actuators that are stuck shut can limit flow enough to create a large temperature differential between flow and return. Systems with multiple zone actuators and no differential bypass are particularly susceptible when actuators are slow to open.
- DHW temperature probe slipped out of position Sometimes
On systems with a hot water cylinder, the probe that runs into the cylinder can slip downwards, meaning it never senses the tank reaching target temperature. The boiler then runs continuously trying to satisfy DHW demand, and the resulting sensor delta across the three measurement points exceeds the allowed threshold, causing a lockout.
- Faulty or poorly seated UBA control board Rare
The UBA (Universal Burner Automaton) is the boiler's primary control module. Bent or misaligned pins on the UBA connector can disrupt sensor signal communication, producing readings the control unit interprets as a sensor mismatch. A faulty UBA itself can also incorrectly prioritise DHW demand and prevent the burner from firing correctly for heating circuits.
How to fix it
- Reset the boiler — no more than two or three times DIY safe
A 2F / 277 lockout requires a manual reset before the boiler will attempt to fire again. You can reset by pressing and holding the up (▲) and down (▼) buttons simultaneously until the flashing 'H' and '!' symbols disappear, or by switching the boiler off at the programmer or boiler switch, waiting 30 seconds, then switching it back on. If the fault returns immediately or after only a short run, do not keep resetting — repeated resets without identifying the cause can mask a developing problem and in some circumstances cause further damage.
- Check that the gas supply is available DIY safe
Confirm that other gas appliances in the property (hob, gas fire) are working normally. If gas is absent from the whole property, contact your gas supplier. Do not attempt to inspect or operate any gas pipework yourself.
- Check system pressure at the gauge DIY safe
With the boiler cold, system pressure should typically read between 1.0 and 1.5 bar on the gauge. If it has dropped below 0.8 bar, use the filling loop to top it up slowly to around 1.2 bar, then close the filling loop valves fully. Low pressure alone is unlikely to cause a 2F fault but should be corrected before calling an engineer.
- Bleed radiators if an airlock is suspected DIY safe
If the system has recently been drained, refilled, or worked on, trapped air is a realistic cause. Use a radiator bleed key to release air from each radiator, starting with those furthest from the boiler and working back. After bleeding, re-check system pressure and top up if needed. For a severely air-bound system, a full purge by an engineer will be more effective.
- Have an engineer test the flow and safety temperature sensors Gas Safe engineer
A Gas Safe registered engineer will use a multimeter to measure the resistance (ohms) of the NTC flow sensor and safety sensor at a known temperature and compare the readings against the manufacturer's specification. A sensor that is open-circuit, short-circuit, or reading outside tolerance should be replaced. The engineer will also inspect the sensor wiring and connectors for corrosion or looseness.
- Have the primary circulation pump inspected and tested Gas Safe engineer
If the sensors test within tolerance, the engineer should check whether the circulation pump is starting up and delivering adequate flow. A seized pump may spin freely by hand when cold but fail under load; an engineer can check pump current draw and observe startup behaviour. If the pump is found to be faulty, replacement is straightforward and cost-effective on most Buderus models.
- Have the DHW cylinder probe position checked Gas Safe engineer
On systems with an indirect hot water cylinder, the engineer should verify that the immersion-style temperature probe is correctly inserted to its full depth and has not slipped down. A probe sitting at the bottom of the cylinder will never sense the stored water reaching its target, keeping the boiler running in DHW mode continuously and generating excessive sensor differentials.
- Have the UBA control board connections inspected Gas Safe engineer
If sensors and pump are both functioning correctly, the engineer should inspect the UBA module's multi-pin connector for bent or misaligned pins, corrosion, or moisture ingress. Reseating the connector or carefully straightening misaligned pins has resolved this fault in documented cases. If the UBA board itself is faulty, replacement will be required.
- Call a Gas Safe registered engineer if the fault persists or returns Gas Safe engineer
All internal boiler work on a gas appliance must be carried out by a Gas Safe registered engineer — this is a legal requirement in the UK. You can verify an engineer's registration at gassaferegister.co.uk. If resets do not clear the fault, or it returns within a short time, book an engineer promptly rather than continuing to reset, as persistent lockouts can indicate a worsening fault.
Parts you may need
- NTC flow temperature sensor · from £25
- NTC safety temperature sensor · from £28
- Primary circulation pump (Buderus compatible) · from £110
- UBA control module / PCB · from £280
- DHW cylinder probe / sensor · from £22
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–£380, depending on the underlying cause.
Frequently asked questions
Can I reset a Buderus 2F / 277 fault myself?
Yes, a single reset is a reasonable first step and is safe for a homeowner to attempt. Press and hold the ▲ and ▼ buttons together until the flashing 'H' symbol clears, or switch the boiler off and on again. If the fault returns after one or two resets, stop resetting and call a Gas Safe engineer — continuing to reset without addressing the underlying cause is not safe practice and can mask a developing problem.
What is the difference between fault codes 2F 271, 2F 274, and 2F 277 on a Buderus boiler?
All three subcodes fall within the same 2F fault family and share the same core meaning: the boiler has detected either an excessive temperature difference between the safety and supply sensors, or a failure to achieve heat rise after the burner starts. Subcode 271 is the most commonly documented and tends to point most directly to sensor differential or heat-rise failure; 274 and 277 are variants within the same diagnostic group. In practice, the troubleshooting approach is identical for all three — sensors are checked first, followed by the circulation pump, then system flow conditions and the control board. Always quote the full code (e.g. 2F 277) to your engineer so they can cross-reference your specific model's service manual.
How much does it cost to fix a Buderus 2F / 277 fault in the UK?
For the two most common causes — a faulty NTC sensor or a failed circulation pump — most people pay between £100 and £380 including parts, labour, and the call-out fee. A sensor replacement with labour typically comes in at around £100–£200, while a pump replacement tends to cost £160–£380. If the UBA control board turns out to be the culprit, costs rise considerably — board replacement can reach £400–£550 once parts and labour are included — but this is a less common outcome. Engineers in London and the South East typically charge 20–30% more than the national average.
Why does my Buderus boiler keep showing 2F even after I've replaced the sensor?
A persistent 2F fault after sensor replacement usually points to the primary circulation pump as the next suspect. If the pump is seized or not starting up reliably, water is not flowing through the heat exchanger and the boiler cannot achieve the expected temperature rise, even with accurate sensors. Other possibilities include a system airlock that was not fully purged, a DHW cylinder probe that has slipped out of position, or — less commonly — a UBA control board with connection or component issues. An engineer should work through each of these systematically.