What does the Vaillant D.90 fault code mean?

Your boiler is currently waiting for the digital control system to finish communicating, which usually means it is temporarily busy rather than broken.

How much does it cost to fix Vaillant error code D.90?

Typical repair cost for the Vaillant D.90 fault is £0-120 including labour.

Vaillant D.90 Fault Code: What It Means & How to Fix It

What the manual says

Manufacturer manual

Digital regulator status

From this model's manual

Verified against the Vaillant/Vaillant Ecotec Plus Pro 839592 05 2006 installation & service manual.

What causes this fault?

This code appears when the boiler's internal computer is trying to pair or exchange data with smart thermostats or external plug-in controls. It occurs because there is a brief delay or 'handshake' process happening between the boiler and the digital programmer. Most of the time, this is simply a temporary status message rather than a permanent hardware failure.

DIY fix possible

Check if any smart thermostats (like Hive, Nest, or vSMART) are currently updating their softwareTurn the boiler off at the main switch, wait 30 seconds, and turn it back onWait 10 minutes to see if the status clears automatically after communication is restored

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Related fault codes

D.91View →F.49View →

All 135 fault codes on the ecoTEC pro 24

Seeing a different code? Every code this model can display, in one place.

35 96 con Connection D,11 D.0 D.1 D.2 D.3 D.4 D.5 D.7 D.8 D.9 D.10 D.12 D.13 D.17 D.18 D.20 D.22 D.23 D.25 D.27 D.28 D.30 D.33 D.34 D.35 D.40 D.41 D.44 D.47 D.50 D.51 D.60 D.61 D.64 D.65 D.67 D.68 D.69 D.70 D.71 D.72 D.75 D.76 D.77 D.78 D.80 D.81 D.82 D.83 D.84 D.91 D.93 D.96 D.97 F.0 F.1 F.10 F.11 F.13 F.20 F.22 F.23 F.24 F.25 F.27 F.28 F.29 F.32 F.49 F.61 F.62 F.63 F.64 F.65 F.67 F.70 F.71 F.72 F.73 F.74 F.75 F.76 F.77 F.78 F70 P.0 P.1 P.2 P.3 P.4 P.5 P.6 S. 2 S. 5 S.0 S.1 S.3 S.4 S.6 S.7 S.8 S.10 S.11 S.13 S.14 S.15 S.16 S.17 S.20 S.21 S.22 S.23 S.24 S.25 S.26 S.27 S.28 S.30 S.31 S.32 S.34 S.36 S.41 S.42 S.52 S.53 S.54 S.96 S.97 S.98

Your boiler is currently waiting for the digital control system to finish communicating, which usually means it is temporarily busy rather than broken.

What the manual says

What causes this fault?

DIY fix possible

Avoid the next call-out bill

Related fault codes

All 135 fault codes on the ecoTEC pro 24

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