Pump overrun time after warm start
The D72 error code on Vaillant boilers indicates pump overrun time after warm start.
Vaillant D72 means: pump overrun time after warm start. The usual causes are (combination boilers only) or charging an, electronically controlled hot water storage through or c1-c2 (system boilers only). You can safely reset the boiler once — if D72 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does D72 Mean
The D72 code is shown by the boiler’s control board when it detects pump overrun time after warm start. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows D72 and the boiler stops until the fault is cleared |
Common Causes
Causes documented in 1 technical sources.
| Cause |
|---|
| (combination boilers only) or charging an |
| electronically controlled hot water storage through |
| C1-C2 (system boilers only) |
| Adjustment range in sec: 0, 10, 20 to 600 Factory setting (when |
| accessories are fitted): 80 Factory setting for system boilers: 300 |
Safety Warning
D72 involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
1. Check if the pump is running — listen for humming. A running pump should be warm but not hot. 2. If the pump is humming but not circulating, it may be air-locked — bleed via the pump bleed screw. 3. If seized, try freeing the impeller with a flat screwdriver through the pump centre spindle (with power off). 4. Check the pump speed setting — it should be appropriate for the system size. 5. Measure the voltage at the pump terminals to confirm the PCB is supplying power. 6. Check for debris in the pump by removing and inspecting the impeller
How to Fix It
Free a seized pump by turning the impeller manually
bleed air from the pump
if the pump motor has failed, replace the pump
flush the system to remove sludge and fit a magnetic filter
replace damaged wiring
Refer to the Vaillant service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Vaillant models that can display fault code D72:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Vaillant models | — | Possible |
Frequently Asked Questions
Free a seized pump by turning the impeller manually. According to the technical documentation, this is the first check on the list for D72.
D72 is not classified as a high-severity fault, so the boiler can be reset once. If D72 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.