What does the Vaillant D.28 fault code mean?

Your boiler is having trouble communicating with an external control or smart home accessory, which might prevent your heating or hot water from turning on correctly.

How much does it cost to fix Vaillant error code D.28?

Typical repair cost for the Vaillant D.28 fault is £120-250 including labour.

Vaillant D.28 Fault Code: What It Means & How to Fix It

What the manual says

Manufacturer manual

Switching accessory relay 2

From this model's manual

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

What causes this fault?

This fault occurs when the boiler's main internal computer loses communication with an external control box or smart home wiring module. The most common reason is a loose connection in the wiring or a technical failure within the accessory module itself that tells the boiler when to turn on and off.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

D.27View →F.27View →F.70View →

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.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.90 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 having trouble communicating with an external control or smart home accessory, which might prevent your heating or hot water from turning on correctly.

What the manual says

What causes this fault?

Engineer required

Avoid the next call-out bill

Related fault codes

All 135 fault codes on the ecoTEC pro 24

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