Viessmann boiler fault codes — what they mean and what to do

What a fault code is telling you

Your Viessmann boiler keeps an eye on itself. When something isn't right, it stops and shows a code on the display so you know roughly what's wrong.

Most codes look alarming but aren't. Some point to simple things you can sort in a few minutes, like low pressure or a one-off glitch.

Others mean a part has failed and needs a Gas Safe registered engineer. We'll always tell you which is which, and never ask you to touch anything to do with gas.

Codes vary a little between Vitodens models, so check your manual for the exact wording. The most common ones are below.

Common Viessmann fault codes

The codes we get asked about most

F4 — no flame detected

This is one most people see. The boiler tried to light and couldn't find a flame, so it shut off to stay safe.

First, check your other gas appliances. If the hob won't light either, it could be your gas supply. Reset the boiler once using the reset button.

If F4 comes straight back, stop there. The ignition or gas valve may need a Gas Safe registered engineer. If you smell gas at any point, call 0800 111 999.

F2 — flame lost during operation

F2 means the boiler lit fine but the flame dropped out partway through. A wobbly gas supply, a blocked flue or tired ignition parts can all cause it.

Reset once and see if it settles. If it keeps coming back, leave it to an engineer — anything touching the gas side or flue isn't a DIY job.

F6 — fan fault

F6 points to the fan not being at standstill, or a plug-in connection to it working loose. The boiler won't fire safely without the fan running right.

You can reset it once, but this one usually needs an engineer to test the fan and its wiring. We'll come and fix it for you.

Safe checks before you call anyone out

These are the only things worth trying yourself. If a code involves gas, skip straight to a Gas Safe registered engineer.

• Check the pressure gauge — it should sit around 1.0 to 1.5 bar when cold.
• Top up via the filling loop if pressure's low, then close the valves fully.
• Make sure the boiler has power and the programmer is set to come on.
• Check your thermostat is calling for heat and the batteries aren't flat.
• Confirm your other gas appliances work, to rule out a wider supply issue.
• In cold weather, check the white external condensate pipe isn't frozen — thaw it gently with warm (not boiling) water if it's safe to reach.
• Reset the boiler once — just once. Don't keep doing it if the code returns.
• If you smell gas, stop everything. Call 0800 111 999, open windows, turn off the gas at the meter only if it's safe to reach, don't touch electrical switches, and leave the house.

Where to look on a Viessmann and how to reset it

Most UK homes with a Viessmann have a Vitodens — the 050-W, 100-W, 111-W or 200-W are the common combi and system models. The fault code shows on the front display, either on the small screen of a 100-W or the larger touch display on a 200-W.

On a Vitodens 100-W, a flashing code with a 'U' symbol means you need to reset by hand once you've sorted the cause; a steady symbol clears itself once the fault is gone. On models with the bigger display, the screen usually tells you the code in words and points you to a reset option.

Reset once, and once only. If the same code returns straight after, that's the boiler telling you the fault is real and still there — repeated resets just hide it. At that point it's time for a Gas Safe registered engineer.

Never attempt anything involving gas, the fan, the flue or internal electrics yourself. Those are engineer jobs, every time.

When a code won't clear — how Smart Plan helps

If you've checked the simple stuff and the code's still there, the next step is a Gas Safe registered engineer. That's where we come in.

Smart Plan is a service plan, not insurance. You've got two easy options when your boiler plays up.

Need it fixed now?

Book a one-off repair and we'll come and fix it for you. One of our Gas Safe registered engineers diagnoses the fault and gets your heating back on.

Want cover for next time?

Take out an ongoing Smart Plan boiler module and you're sorted when the next code appears. Parts and labour are included up to your cover limit.

Cover is modular, so you only pick what you want — don't pay for what you don't use. Boiler cover runs up to £500 per year if your boiler's under 7 years old, or up to £200 if it's older. A £95 call-out fee applies.

We've looked after over 15,000 customers, we've been trading since 2014, and we're rated on Trustpilot. When a fault code won't budge, we'll come and fix it for you.

Viessmann fault code FAQs

Code still showing? We'll come and fix it for you.

Book a one-off repair or set up an ongoing Smart Plan boiler module. A service plan, not insurance — parts and labour included up to your cover limit.

Helpful links

• No heating? Book a repair
• Boiler & central heating cover
• More boiler guides on the blog
• Check an engineer on the Gas Safe Register