Viessmann E5 Fault Code: Causes, Fixes & Repair Costs
What does the Viessmann E5 fault code mean?
The E5 fault code on Viessmann boilers has two distinct meanings depending on your specific model. On the Vitodens 200, it signals that the boiler has entered emergency mode or is cooling down because of an internal BUS fault — a breakdown in the communication network that links the boiler's control components. This can also cause the circulation pump to run at maximum speed due to an open circuit. On the Vitodens 222-F, E5 means the burner is blocked: the boiler water temperature is too high and needs to reduce, with air being vented automatically. It can also point to a fault within the burner control unit. Because the meaning differs between models, it's important to identify your boiler before proceeding with any diagnosis.
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
- Internal BUS wiring fault or loose connection Common
On the Vitodens 200, the BUS is the internal data network connecting the boiler's control boards. A corroded terminal, damaged cable, or loose plug anywhere along this network can break communication, triggering E5. This is the most frequently diagnosed root cause on the Vitodens 200 range.
- Circulation pump failure or airlock Common
If the pump is seized, running erratically, or has an airlock, water cannot circulate at the required flow rate. The Vitodens 200 specifically flags this scenario — including where the pump runs at maximum speed due to an open circuit — as an E5 condition. Sludge build-up from an unserviced system is a common contributing factor.
- Blocked heat exchanger or restricted flow Sometimes
On the Vitodens 222-F in particular, restricted water circulation through a sludge-laden or partially blocked heat exchanger can cause temperatures to rise, prompting the burner to lock out and the E5 code to appear.
- Faulty PCB or control unit Sometimes
The PCB manages BUS communication on the Vitodens 200. If it is failing, it may misread or drop signals, causing intermittent or persistent E5 faults that don't clear with a reset. On the Vitodens 222-F, a fault within the burner control unit can also produce this code.
- Faulty flow switch or incorrect flow direction Rare
A defective flow switch, incorrectly plumbed pipework, or an obstruction preventing adequate flow rate can stop the boiler from confirming safe circulation, leading to E5 on some Vitodens 200 installations.
How to fix it
- Check your boiler model first DIY safe
Locate the model label on your boiler — usually on the front panel or inner casing. Confirming whether you have a Vitodens 200 or Vitodens 222-F helps narrow down whether E5 relates to a BUS/pump fault or a burner blockage, and will help any engineer you call diagnose it faster.
- Verify your gas, electricity, and water supplies DIY safe
Test that other gas appliances in your home (a hob or gas fire) are working normally. Check that the boiler has mains electricity and that your cold water supply hasn't been interrupted. Ruling out a supply problem first avoids unnecessary call-outs.
- Check system pressure DIY safe
Look at the pressure gauge on the boiler. Most Viessmann models operate correctly between 1 and 1.5 bar, shown as the green zone on the gauge. If pressure has dropped below 1 bar, top it up using the filling loop until it sits within the green zone, then attempt a reset.
- Attempt a single boiler reset DIY safe
Consult your boiler's user manual for the reset procedure (typically holding the reset button for a few seconds). Attempt this once. If E5 clears and the boiler fires up normally, monitor it over the next few hours. If the fault returns, do not keep resetting — repeated resets without fixing the underlying cause can mask a more serious problem.
- Call a Gas Safe registered engineer for internal inspection Gas Safe engineer
If E5 persists or keeps returning, the fault requires professional diagnosis. An engineer will inspect the BUS wiring and terminals for corrosion or damage, test the circulation pump for seizure or airlock, check flow rates and the flow switch, inspect the heat exchanger for sludge, and test the PCB or burner control unit. Viessmann offers fixed-price repairs — you can contact their Customer Care team on 01952 675000 to enquire.
Parts you may need
- Circulation pump · from £120
- PCB / control board · from £280
- BUS communication cable / wiring harness · from £45
- Flow switch · from £55
- Burner control unit (Vitodens 222-F) · 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–£400, depending on the underlying cause.
Frequently asked questions
Why does E5 mean different things on different Viessmann boilers?
Viessmann uses a shared fault code library across its range, but the internal systems those codes map to differ by model. On the Vitodens 200, E5 is tied to the BUS communication network and pump circuit; on the Vitodens 222-F, it relates to the burner being blocked or the burner control unit. This is why Viessmann themselves recommend using a Viessmann-trained installer — they'll know which diagnostic path to follow for your specific model.
Can I keep resetting the boiler to clear E5?
A single reset is worth trying, but repeated resets are not advisable. If the underlying fault — whether a damaged BUS cable, a struggling pump, or a blocked heat exchanger — hasn't been fixed, the code will return. Continually resetting can also delay diagnosis and, in some fault scenarios, cause additional wear. If E5 comes back after one reset, call an engineer.
How much does it typically cost to fix a Viessmann E5 fault?
Most E5 repairs fall in the range of £120 to £400, covering the engineer's time and the most commonly replaced parts such as the circulation pump or BUS wiring. A pump repair or unblocking tends to sit at the lower end (around £100–£250), while pump replacement usually costs £200–£400 including labour. If the PCB or burner control unit is at fault, costs can rise to £300–£600 or more. In rare cases where the boiler is beyond economical repair, full replacement starts from around £2,100. A standard Viessmann service costs £80–£130 and can prevent many of these faults from developing.
Does an E5 fault affect my Viessmann warranty?
It can do indirectly. Viessmann warranties typically require annual servicing by a qualified engineer. If your boiler hasn't been regularly serviced and a fault develops — including E5 — your warranty or extended guarantee may not cover the repair. Keep records of annual services to protect your warranty entitlement. If you're unsure of your warranty status, contact Viessmann on 01952 675000.