Worcester Bosch H09 fault codewhat it means and how to fix it
The control board has lost its data link to the pump. The boiler keeps running, but Worcester flag it because a pump the board cannot talk to is either wired wrongly or the wrong pump.
Take care
Get a Gas Safe registered engineer to look at your Worcester Bosch H09
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What H09 means
H09 is one of the Greenstar i ErP maintenance codes, and Worcester use it as their worked example of what an H code is: "communications to the pump has failed. The feedback signal has been lost, possible causes are electrical connections loose or disconnected, pump has been replaced with an incorrect type". The Greenstar i uses a modulating pump that the control board drives over a signal lead as well as the mains lead, varying its speed to suit the demand and reading back a feedback signal that confirms it is doing so.
H09 means that feedback has stopped. The pump may well still be running — the mains supply to it is separate — but the board has no idea at what speed, and it logs the loss as a maintenance message rather than a fault, so the boiler carries on rather than locking out.
The remedy row is short: check the electrical connections are fitted correctly, check the correct pump has been fitted, and once checked, re-power the appliance to test the communications again. That second check is the one that catches people. A pump replaced with a generic unit, or with a Worcester pump from a different range, can move water perfectly well and still never answer the board. The code is only on ranges whose pump talks back; the CDi Classic drives its pump directly and has no equivalent, and a pump that has stopped altogether on any range shows as A1 or as an overheat rather than H09.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Pump signal lead disconnected | The low-voltage control lead to the pump has a separate plug from the mains lead and is easily left off after the pump or hydraulic block has been out. | Common |
| Wrong replacement pump | Worcester name this cause. A pump without the matching control interface runs but does not communicate, and the board logs H09 from the first cycle. | Common |
| Pump electronics failed | The pump's own control module can fail while the motor still turns, silencing the feedback signal. | Occasional |
| Control board fault | Rarely, the board's pump interface fails. It is diagnosed by elimination after the lead and pump have been proven. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£90–£450
Time on site
45 minutes
Reconnecting the signal lead £90–£140. Correct replacement pump £280–£450 if the wrong one was fitted.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Central heating circulating pump
CH-PUMP-15-60£90–£180Plumbing merchant
Price checked 28 September 2026
Worcester Bosch Greenstar control board (PCB)
£250–£450Authorised Worcester parts distributor
Price checked 28 September 2026
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Related Worcester Bosch fault codes
- A8Get it checkedThe boiler has lost communication with a Worcester control on the two-wire bus — a Sense, FX or FW controller, or a Wave thermostat. Heating usually carries on at the boiler's own settings.Related: electronics and communication
- A6Get it checkedThe boiler thinks an external limit thermostat has opened — usually the underfloor heating stat — or the link that stands in for one is missing. Nothing runs until that circuit is closed again.Related: electronics and communication
- EA 227Stop — call an engineerThe boiler tried to light and never detected a flame, so it has shut the gas off and locked out. This is the most common Worcester fault code.Related: same brand
- CE 207Get it checkedSystem water pressure has dropped too low for the boiler to run safely. Topping the system back up to 1.2 bar usually clears it in five minutes.Related: same brand
- E9 219Stop — call an engineerThe boiler has overheated and the safety thermostat has tripped. Water is not carrying heat away from the exchanger, and it should not be run until that is fixed.Related: same brand
- C6 224Get it checkedThe fan is not reaching the speed the boiler asked for, so combustion cannot be confirmed as safe and the burner has been prevented from firing.Related: same brand
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Related guides
Common questions about Worcester Bosch H09
Is the pump broken?
Not necessarily. H09 is about the signal between board and pump, not about whether the pump turns. If the pump had stopped you would see A1 281 or an overheat code instead.
The heating still works. Can I ignore it?
For a short while, but not indefinitely. Without feedback the board cannot modulate the pump, so the boiler runs less efficiently and less quietly than designed, and the message will keep returning until the cause is found.
Why does it show as H09 and not a fault code?
Because Worcester classify a lost pump signal as something that needs attention rather than something that stops the appliance. That is the definition of their H codes.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.