What it means
What D5 is telling you
D5 is a control board fault — the boiler's electronics have either failed a self-check or lost communication with a component they expect to talk to.
Before condemning a PCB we always check the simple things, because damp, a poor earth or a corroded connector produces the same code as a genuinely dead board.
Water ingress is a surprisingly common cause: a small leak from above dripping onto the board will do it, and replacing the board without fixing the leak just kills the new one too.
Before you call
Safe checks you can do yourself
- Turn the boiler off at the fused spur for two minutes, then back on
- Look for any sign of water dripping onto or around the boiler
- Reset once — if D5 returns immediately, it needs diagnosing properly
Never remove the boiler casing or work on the sealed combustion chamber yourself — by law that’s Gas Safe registered engineers only. If you smell gas, call 0800 111 999 immediately.
How we fix it
What we do on the visit
- Full electrical diagnosis before any board is quoted
- Connectors, earth and wiring loom checked for corrosion and damp
- Any water ingress traced and fixed first
- PCB replaced and correctly configured to your appliance where it has genuinely failed
How urgent is it?
No heating or hot water. Book a diagnostic visit — this one needs test equipment.
Costs
What a repair costs
Our diagnostic visit is £99 inc VAT and it comes off the bill if we carry out the repair. We give you a fixed price before touching anything — no hourly rates, no surprises on the invoice.
We’re Gas Safe registered, Which? Trusted Trader endorsed and rated 4.9 across 206+ reviews. We carry the common Worcester Bosch and Viessmann spares on the van, so most faults are fixed on the first visit rather than booked back in.
Common questions
How much is a Worcester PCB replacement?
PCBs are one of the dearer parts, commonly £400–£650 inc VAT fitted. That's the point where we'll be straight with you about repair versus replacement.
Is a D5 fault always the PCB?
No, and that's why the diagnostic matters. We regularly find damp connectors or a failed sensor giving a D5 on a perfectly good board.
Should I replace the boiler instead?
If the boiler is over about 12 years old and the PCB is £550, a new Worcester or Viessmann with a 10–12 year guarantee usually makes more sense. We'll give you both prices and no pressure.
Book it in
Get an engineer out
Step 1 / 5
60 second boiler quote
No callbacks unless you want one
What can we help with?
Pick the option that fits — we'll tailor the next questions.
More help