A D5 on a Worcester Bosch usually means the condensate is not draining away properly, and on most boilers that comes down to a blocked or frozen condensate pipe. We’re Clever Energy Boilers, Gas Safe registered and accredited Worcester Bosch installers based in Bingley, working across Yorkshire and the Humber, the North West and the Midlands. If your Worcester is an older boiler that keeps showing error codes, a replacement Worcester Bosch is the better option longer term for efficiency and to save on repair bills.
The good news is that D5 is among the friendliest codes to deal with. Plenty of homeowners clear it in ten minutes with a jug of warm water. We’ll walk through how, and explain the one model where the meaning is a little different.
What does the D5 error code mean on a Worcester Bosch boiler?
A condensing boiler turns the steam in its exhaust back into water, and that water has to leave through a small plastic pipe. If it can’t, the boiler backs up and shuts down. Most sources say D5 signals a blocked or frozen condensate pipe. On the CDi Highflow, though, D5 is listed as a condensate pump failure, because that model uses a pump to move the water.
Check your model before assuming it’s a frozen pipe. If your boiler has a pump (you’ll see a small unit with a tank near the boiler), the pump may be the cause.
What makes the condensate pipe block or freeze and trigger a Worcester fault?
- Freezing temperatures, especially where the pipe runs outside or has a long horizontal stretch
- A pipe that sags, letting water pool and freeze
- Debris, limescale or algae building up inside
- A trap that has silted up
- A failed condensate pump on models that use one
How do I fix a Worcester D5 error safely?
Cold weather is the usual story, so start there.
- Switch the heating off and wait a few minutes.
- Trace the condensate pipe outside. It’s a plastic pipe, often 21.5mm, that runs from the boiler to a drain or gully.
- Look for ice, usually at the end of the pipe or on a bend. You may hear gurgling from the boiler too.
- Pour warm water, never boiling, along the pipe, working from the end towards the boiler.
- Wait ten minutes, then press reset on the boiler.
Wear gloves and take care on frozen steps and paths. If you can’t reach the pipe safely, leave it. Our condensate pipe guide shows the process in more detail.
What if the pipe was not frozen when the Worcester D5 fault appeared?
Check the pipe for a visible blockage at the end, a kink, or a sagging section collecting water. Beyond that, the trap and pump are inside the boiler, and that’s a job for a Gas Safe registered engineer. Don’t take the casing off.
One more sensible check: glance at the pressure gauge. A cold system should read about 1 to 1.5 bar. If it’s low, switch the boiler off, connect the filling loop, open the valves slowly to bring the pressure up, and close them again.
Why does the D5 fault code keep returning on my Worcester every cold snap?
If it happens each winter, the pipe is probably badly routed: too long, too exposed, or running uphill. Insulating it with weatherproof lagging helps, but a pipe that keeps freezing often needs rerouting to a drain indoors. That’s something to discuss with an engineer or with the installer of a new boiler.
Is the Worcester D5 error dangerous?
No. Blocked condensate stops the boiler firing, which is a safety response. There’s no particular risk, but if you smell gas, switch nothing on and call 0800 111 999.
Does a D5 fault mean I need a new Worcester Bosch boiler?
Not usually. A new installation does give you a chance to fix the cause properly, though. On an older Worcester, if you’re clearing condensate or other codes every winter, replacing the boiler with a modern Worcester Bosch lets us route the pipe sensibly, and you’ll get better efficiency into the bargain. It tends to pay off once the boiler is past 8 years.
Fitting a new Worcester Bosch with Clever Energy
We install across Yorkshire and the Humber, in towns such as Keighley, Halifax, Harrogate and York, across the North West from Bolton and Oldham to Stockport and Wigan, and throughout the Midlands. Read about our Worcester Bosch boiler installation or see your price online. To talk through a new boiler, call 0330 055 2210 between 8am and 8pm on weekdays, or 10am to 4pm at the weekend.
Worcester Bosch D5 fault code FAQs
Is a Worcester D5 error always a frozen condensate pipe?
No. It’s the most common cause, but on the CDi Highflow it refers to a condensate pump failure. Check which model you have.
Can I use boiling water to thaw the pipe and clear the fault?
No. Boiling water can crack the plastic pipe. Warm water is enough.
How long should I wait after thawing before resetting the Worcester?
About ten minutes, then reset the boiler once. If it fires up normally, you’re done.
Why is the D5 error code only a winter problem for my Worcester?
Because the pipe freezes when temperatures drop. In summer the same pipe flows freely.
Will lagging the pipe stop the Worcester fault returning?
It helps a lot, but if the pipe is long or poorly sloped it may still freeze. Rerouting is a more permanent fix.
More Worcester Bosch error codes
D5 is closely related to the frozen-pipe fault. Before this one, have a look at the Worcester Bosch 229 fault code; after it, the Worcester Bosch A1 fault code covers the next code in the set. The full list sits on our Worcester boiler error codes guide.
