Worcester Bosch Greenstar CDI C6 fault code

Worcester Bosch Greenstar CDI C6 fault code explained

Whilst the C6 fault code is probably not the most common, if you have a Worcester Bosch Greenstar CDI boiler you may experience this fault code at some point.

This fault code will cause your Worcester Bosch boiler to stop working, leaving you without central heating or hot water.

If you look in the Worcester Bosch CDI installation manual under the C6 fault code it states the following;

“Fan speed too low – Check: fan lead and connector, and fan; replace as necessary”

All Worcester Bosch Greenstar boilers have a fan. The fan only has one job to do, but it is one of the most important components on a boiler.

If you are seeing the C6 fault code on your Worcester Bosch boiler it more than likely means that the fan has failed.

Sometimes you may be able to get your boiler working intermittently with a reset, but most of the time a C6 fault code will not reset and your boiler will not work at all.

Fans on modern gas boilers with premix burner designs like the Worcester Bosch CDI, have sophisticated electronics which communicate back to the printed circuit board(PCB).

The printed circuit board controls the speed of the fan and modulates its speed depending on the load on the boiler.

If the fan isn’t running at all or at the right speed, the printed circuit board will know this and shut the boiler down with an C6 fault code as a safety precaution.

The fan operating correctly is crucial to the boiler working properly, and any irregutlatires detected with the speed of the fan will cause the boiler to shut down with the C6 fault code.

Unlike a lot of fault codes on Worcester Bosch boilers, the C6 fault code is very specific and is trying to tell you that the fan has failed, as opposed to just pointing you in the right direction.

In our experience working on Worcester Bosch CDI boilers, the number one cause of the C6 fault code nine times out of ten is the fan.

The fan can fail in a few different ways but mostly the electronic printed circuit board on the fan just fails.

When to call a gas engineer to fix your boiler

If you are experiencing the C6 fault code on your Worcester Bosch boiler, it is important to take action as soon as possible.

While some issues can be resolved by homeowners themselves, others require the expertise of a qualified Gas Safe registered heating engineer.

The C6 fault code is usually caused by a faulty fan, but it could be caused by a faulty printed circuit board or faulty wiring harness.

This is why it is extremely important to get a suitable heating engineer with experience on Worcester Bosch boilers, otherwise you could end up wasting money fitting parts to your boiler that are unnecessary.

With some fault codes you can often reset your boiler to get it going short term, but this is generally not the case with the C6 fault code. Once you see this fault code it won’t go away without a repair.

So it usually best to get a qualified Gas Safe registered heating engineer to have a look at your boiler at your earliest convenience.

How to prevent the C6 fault code

A lot of the time certain faults on a Worcester Bosch Greenstar CDI boiler can be prevented with regular annual servicing and maintenance. Unfortunately this is not the case with the C6 fault code.

A lot of the parts on a Greenstar CDI boiler are non serviceable parts, this includes the fan as well. This means that there is nothing that can be done to these parts to extend the life of the fan and prevent the C6 fault code.

The only thing that can help to prevent seeing the C6 fault code is to avoid turning your boiler off unnecessarily.

Sometimes when people go on holiday they like to turn their boilers off electrically. This is a bad idea. It’s best just to isolate your boiler hydraulically by turning the mains water off, but it’s best to leave the power switched on to your boiler.

This is because sometimes the electronics inside the fan fail when getting powered back on. This is some inherent design flaw within the electronics on these fan and whilst the exact cause of failure is not important, it’s just important to know to avoid turning your boiler off unnecessarily.

This fan failure problem also affects the other Worcester Bosch Greenstar boilers that use the same fan as the CDI model. These include the 24i and 28i Junior, 25Si and 30Si combination boilers and the Ri heat-only boilers as well.

It’s also worth noting that sometimes engineers just servicing a Worcester Bosch boiler that uses one of these fans, will experience the C6 fan failure fault simply by turning the power off to service the boiler.

This is not the engineers fault it’s just bad luck. A lot of engineers who have experienced this issue will try avoid turning the power to the boiler off whilst servicing it just to avoid this problem.

However it’s not really practical or safe to service a Worcester Bosch Greenstar CDI boiler without turning the power off.

Worcester Bosch Greenstar CDI boilers affected by the C6 fault code

The C6 fault code on Worcester Bosch CDI boilers can affect any combination boiler or system boiler.

Below is a list of Worcester Greenstar CDI boilers that can be affected by the C6 fault code;

• Greenstar Classic 25 CDI, 29 CDI, 34 CDI, 38 CDI and 42 CDI combination boilers
• Greenstar Classic ErP 29 CDI, ErP 34 CDI, ErP 38 CDI and ErP 42 CDI combination boilers
• Greenstar 30 CDI and 40CDI conventional system boilers

Frequently asked questions:

Is my boiler showing an C6 fault code worth repairing ?

Yes definitely, most of the time your broken Worcester Bosch CDI boiler displaying an C6 fault code will be worth repairing.

Obviously the cost to repair your boiler will be determined by which parts need to be replaced.

You would need a competent, Gas Safe registered heating engineer to have a look at your boiler and make an assessment to determine exactly which parts might need to be replaced.

Before replacing your boiler it is always worth getting a suitable Gas Safe registered heating engineer, with experience working on Worcester Bosch boilers, to make an assessment of your boiler so you can determine whether it is worth fixing not.

Can I repair the C6 fault code myself?

Most of the time an end user will not be able to solve the C6 fault code in any way, even by resetting the boiler.

Fixing the C6 fault code will usually require removing the cover of your boiler to replace parts which you are not legally allowed to do unless you are a Gas Safe registered heating engineer.

Is the C6 fault code dangerous?

No definitely not , the C6 fault code on a Worcester Bosch CDI boiler is not inherently dangerous, it’s the opposite.

Modern Worcester Bosch boilers are designed with fail safes in place to make sure that the boiler will only work if it safe to do so.

If you are having issues with an intermittent C6 fault code, resetting the boiler is often only a short term solution to your problem, and your boiler may stop working altogether at some point.

As such if your boiler is coming up with an C6 fault code, the best thing to do it get it repaired at your earliest convenience, by a suitable Gas Safe registered heating engineer – ideally one that has experience working on Worcester Bosch boilers.