Worcester Bosch C7 fault — what it means and what to do

What does the Worcester Bosch C7 fault mean?

The Worcester Bosch C7 fault means the fan inside your boiler isn't running, or the control board isn't getting a signal to confirm it's spinning. Before it lights, your boiler runs the fan to clear the flue of any old combustion gases. If the fan doesn't turn, the boiler locks out and refuses to fire — on purpose, to keep you safe.

The sub-code beneath it tells you more: C7 214 means the fan isn't running at all on start-up, and C7 216 means it's running but too slowly. Either way, you'll have no heating and no hot water until it's looked at.

This is an engineer-only fix. It usually points to a failed fan, loose wiring between the fan and the board, a blocked flue, or the board itself. None of those are safe for you to touch — but there are a couple of quick checks you can do first, and we'll walk you through them below.

Codes vary a little between Greenstar models — on some older CDi boilers a dead or slow fan shows as C6 instead. Check your manual for the exact wording, then read the C6 vs C7 section below to be sure which one you've got.

Worcester Bosch C7 — the key facts

What causes the C7 fault?

C7 is a fan and airflow fault, so the cause is usually somewhere in that circuit. Here are the common ones, roughly in order of how often they turn up.

1. A failed fan

The most common cause is the fan itself — worn bearings, a seized motor, or an electrical failure inside it. If the fan can't spin up, the boiler never gets the green light to fire.

2. Loose or damaged wiring

The fan talks to the control board through a small connector and harness. If that's worked loose, corroded, or chafed, the board can't read the fan speed and throws a C7 even when the fan is fine.

3. A blocked or obstructed flue

Debris, soot, ice or even a bird's nest in the flue can throw the airflow off and pull the fan out of range. This one's worth a quick look from outside (see the safe checks below) before you assume the worst.

4. A faulty PCB (control board)

Sometimes the fan is perfectly healthy and it's the board that's misreading it. This is the pricier outcome, and only an engineer can tell it apart from a fan fault with proper testing.

5. The air-pressure sensor

A split or blocked sensing tube, or a faulty air-pressure switch, can feed the board the wrong reading and mimic a fan fault. It's a common real cause that's easy to miss without the right kit.

C7 symptoms and likely causes

C6 vs C7 — which fan fault do I have?

C6 and C7 are siblings — both are fan faults — but they're not the same thing, and people mix them up all the time. Here's the simple way to tell them apart.

C7 = the fan isn't spinning

C7 means the fan isn't running, or the board isn't getting a feedback signal at all. C7 214 is "fan not running on start-up"; C7 216 is "fan speed too low". The give-away is silence — you don't hear the fan spin up when the boiler tries to fire.

C6 = the fan is spinning at the wrong speed

C6 means the fan is running but at the wrong speed — either too fast or too slow — rather than not running at all. So with C6 you can often hear the fan; with C7 you usually can't. The repair suspects overlap (fan, wiring, board), and the cost range is similar, but the code tells the engineer where to start. The exact sub-code direction varies by model, so check your manual.

One-liner: C7 = fan not spinning; C6 = fan spinning wrong. If your display actually shows C6, read our C6 fan fault guide instead — it covers the same fixes for the speed-too-high and speed-too-low side.

How do I fix the C7 fault — and what's safe to do myself?

There's a clear line here. A couple of checks are safe for you. Everything past that needs a Gas Safe registered engineer, because it means opening a sealed combustion chamber and working near 230 volts — never DIY gas work.

Safe to do yourself

Reset the boiler once. Switch it off at the wall for about 30 seconds, or press the reset button per your manual, and let it try again. Just the once.

Listen for the fan. When it tries to start, can you hear it spin up? Silence usually means a true fan fault.

Check your pressure. Make sure the gauge sits around 1.0 to 1.5 bar when the boiler's cold — low pressure is its own problem, but it's worth ruling out.

Look at the flue outside. From the ground, check the external flue terminal for an obvious blockage — leaves, debris, ice, or a bird's nest. Just look; don't poke around or dismantle anything.

Leave this to a Gas Safe registered engineer

Opening the boiler casing, testing voltages, replacing the fan, diagnosing or swapping the board, rewiring connectors, clearing the internal flue, or checking the air-pressure circuit. All of it sits on the boiler's flue-safety path, so it's an engineer's job — and it's exactly what we'll come and do for you.

Whatever you do, don't keep resetting it

If C7 comes straight back after one reset, stop. Hammering the reset button won't fix a dead fan or a loose wire — it just hides the fault and can cause more damage. One reset, then book an engineer.

Is the C7 fault dangerous, and is it an emergency?

C7 is not a gas emergency in itself. The boiler has spotted a problem and shut itself down — that's the safety system doing its job, not a sign of immediate danger. It's safe to leave the boiler switched off until an engineer can come.

The National Gas Emergency line, 0800 111 999, is only for when you can smell gas or your carbon monoxide alarm is going off. A C7 code on its own is not a reason to call it. If you ever do smell gas, that's different — open the windows, turn the gas off at the meter, don't touch electrical switches, leave the house, and call 0800 111 999.

The reason C7 forces a hard lockout rather than just letting you restart is simple: the fan clears the flue before the boiler lights. Without proven airflow, combustion gases could build up, so the boiler refuses to fire until the fault is fixed. That's why repeatedly resetting it is the wrong move.

How much does it cost to repair a C7 fault?

As a rough industry guide, a C7 repair typically lands somewhere between £150 and £400, depending on what's actually wrong. These are typical UK ranges to set your expectations — not Smart Plan prices, and they vary by region, model and parts availability.

A loose-wiring repair or a simple flue clear is the cheapest outcome, often around £80–£150. A fan replacement — the most common fix — is usually somewhere around £225–£375 all in, with the part itself often £100–£220 and the rest labour. The expensive outlier is a faulty control board, which can run from roughly £180 to £300-plus for the part.

If you've got a Smart Plan boiler module, parts and labour are included up to your cover limit, so a C7 repair is handled for you rather than landing as a surprise bill. A £95 call-out fee applies. More on how that works below.

Repair or replace?

A single fan or wiring fix on a newer boiler is almost always worth repairing. The rule of thumb engineers use: if the repair quote creeps past about half the cost of a new boiler — say a pricey board on an older unit that's already needed other work — replacement may be the smarter spend. If your boiler's over 10 years old and breaking down regularly, it's worth getting that conversation going.

Worcester Bosch C7 fault FAQs

C7 won't clear? We'll come and fix it for you.

Once you've done the safe checks and C7 is still showing, 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. Book a one-off repair and we'll send a Gas Safe registered engineer to diagnose the fault and get your heating back on. Or take out an ongoing Smart Plan boiler module so you're sorted next time too, with parts and labour 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're from UK Boiler Company Ltd, trading since 2014, and we're rated on Trustpilot. When a fault code won't budge, we'll come and fix it for you.

Boiler showing C7? Let us take care of it.

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, with a £95 call-out fee.

Helpful links

• All Worcester Bosch fault codes explained
• C6 fault — fan speed fault (the C7 sibling)
• No heating? Book a repair
• Boiler & central heating cover
• More boiler guides on the blog
• Check an engineer on the Gas Safe Register