Vaillant
The Vaillant ecoTEC plus 612 is a 12 kW natural gas or LPG system boiler with a 91.2% seasonal efficiency, designed for wall-hung installation in UK homes.
The Vaillant ecoTEC plus 612 is a wall-hung condensing system boiler designed for domestic heating installations in the UK. This appliance provides a maximum central heating output of 12 kW, making it suitable for properties requiring a moderate heat load. Engineers can find comprehensive technical specifications, installation guidelines, and fault code diagnostics within this reference. Homeowners can also access essential information regarding their heating system.
Stick a QR tag on the case, scan it on every service and give your customer a permanent, shareable service history they can pull up from any phone.
Permanent, shareable service history
One QR scan on the boiler surfaces every previous fault, part change and visit — no paperwork to dig out.
Free AI fault diagnostics, built in
Every tag you fit unlocks the AI diagnostic tool for that exact model — paste a fault code, get a ranked cause list.
Your name on the boiler forever
When the next service or breakdown comes around the homeowner scans and sees your number first.
First 12 BoilerTags are free
Tag every install and service you do from now on — the subscription only kicks in once you scale past your first dozen.
Diagnosing a fault on a Vaillant ecoTEC plus 831 Propane right now?
Try the free AI fault diagnostics tool — no signup needed.
Full technical specifications extracted from the manufacturer brochure. Empty sections are hidden.
pH value between 6.5 and 8.5 for systems with aluminium
For the 2nd year of the guarantee to be valid an annual service must be carried out by a competent person approved at the time by the Health and Safety Executive one year after installation.
The Vaillant ecoTEC plus 612 is a natural gas system boiler, also compatible with LPG, offering a nominal central heating output of 12 kW and a minimum output of 4.9 kW. It achieves a seasonal efficiency of 91.2% and is classified as a Class 5 NOx appliance. The boiler incorporates an aluminium primary heat exchanger and a modulating pump with two speed settings, providing an available head of 2.5 metres. Physical dimensions are 720mm high, 440mm wide, and 335mm deep, with a dry weight of 35 kg. Standard warranty coverage is 2 years, subject to annual servicing by a competent person for the second year's validity. Installation requires specific clearances and adherence to water quality guidelines, with a pH value between 6.5 and 8.5 for systems containing aluminium components. The appliance is designed for wall-hung mounting and includes integrated frost protection.
Every fault code listed in the manufacturer brochure, with likely causes and engineer actions. Each code has a permalink — paste a URL like https://www.boilertag.com/boilers/vaillant/ecotec-plus-831-propane#fault-f. 0 to jump straight to the entry.
| Code | Meaning | Details |
|---|---|---|
| F. 0 | Flow-NTC open circuit Show causes & actionsLikely causes
| Details |
| F. 1 | Return-NTC open circuit Show causes & actionsLikely causes
| Details |
| F.10 | Flow NTC short circuit Show causes & actionsLikely causes
| Details |
| F.11 | Return NTC short circuit Show causes & actionsLikely causes
| Details |
| F.13 | Tank NTC short circuit Show causes & actionsLikely causes
| Details |
| F.20 | Safety temperature limiter by NTC activated Show causes & actionsLikely causes
| Details |
| F.22 | Dry fire Show causes & actionsLikely causes
| Details |
| F.23 | Water shortage, temperature difference between flow and return NTC too large Show causes & actionsLikely causes
| Details |
| F.24 | Water shortage, temperature rise too quick Show causes & actionsLikely causes
| Details |
| F.25 | Interruption in the compact thermal module cable harness Show causes & actionsLikely causes
| Details |
| F.27 | Incorrect sensing of flame Show causes & actionsLikely causes
| Details |
| F.28 | Appliance does not start: Attempts to ignite during start failed Show causes & actionsLikely causes
| Details |
| F.29 | Flame goes off during operation and subsequent ignition attempts failed Show causes & actionsLikely causes
| Details |
| F.32 | Fan speed variation Show causes & actionsLikely causes
| Details |
| F.49 | eBUS undervoltage Show causes & actionsLikely causes
| Details |
| F.61 | Gas-valve control defective Show causes & actionsLikely causes
| Details |
| F.62 | Gas valve shutoff delay Show causes & actionsLikely causes
| Details |
| F.63 | EEPROM error Show causes & actionsLikely causes
| Details |
| F.64 | Electronics/NTC fault Show causes & actionsLikely causes
| Details |
| F.65 | Electronics temperature too high Show causes & actionsLikely causes
| Details |
| F.67 | Flame detector input signal is outside the limits (0 or 5 V) Show causes & actionsLikely causes
| Details |
| F.70 | No valid DSN in display and/or mainboard Show causes & actionsLikely causes
| Details |
| F.71 | Flow NTC reports constant value (stuck at) Show causes & actionsLikely causes
| Details |
| F.72 | Flow and/or return NTC fault Show causes & actionsLikely causes
| Details |
| F.73 | Water pressure sensor signal out of range (too low) Show causes & actionsLikely causes
| Details |
| F.74 | Water pressure sensor signal out of range (too high) Show causes & actionsLikely causes
| Details |
| F.75 | No pressure rise was detected on turning on the pump Show causes & actionsLikely causes
| Details |
| F.76 | Overheating protection on primary heat exchanger triggered Show causes & actionsLikely causes
| Details |
| F.77 | condensate pump or feedback of accessorie blocks heating Show causes & actionsLikely causes
| Details |
| F.78 | wrong configuration with accessory Show causes & actionsLikely causes
| Details |
| con | no communication to mainboard Show causes & actionsLikely causes
| Details |
Patterns that group across the manufacturer's fault-code table. Each entry links to the full code listing further down the page.
Triggered by fault code F. 0.
Triggered by fault code F. 1.
Triggered by fault code F.10.
Triggered by fault code F.11.
Triggered by fault code F.13.
Diagnostic checklists from engineer-submitted Vaillant faults, with step-by-step checks and safety notes.
The Vaillant ecoTEC plus 610 displaying fault code F.040 indicates that the air ratio is too low, often due to a fault in the flue gas…
The Vaillant ecoTEC plus 610 displaying fault code F.028 indicates an ignition failure, meaning the boiler failed to ignite or detect a…
Common questions from engineers and homeowners about the Vaillant ecoTEC plus 831 Propane.
We hold the Vaillant ecoTEC plus 831 Propane manual — and every other UK boiler and heat pump brochure. Sign up and pull any model up from your phone, on the job.
Sign up to access brochuresTag it before you leave. Next scan shows every service, fault and part change — and the AI diagnostic tool is free on every tag you fit.
Specifications on this page are extracted from the manufacturer brochure. Always cross-check against the latest datasheet before commissioning or quoting. Last updated 28 June 2026.