What does the Vaillant S.98 fault code mean?

Your boiler is temporarily paused because it has detected a potential issue with its internal sensors while performing a self-test.

How much does it cost to fix Vaillant error code S.98?

Typical repair cost for the Vaillant S.98 fault is £90-180 including labour.

Vaillant S.98 Fault Code: What It Means & How to Fix It

What the manual says

Manufacturer manual

Flow-/Return-sensor check is running, demand (DHW or heating) is blocked

Shared across the range

This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s manual.

What causes this fault?

This fault occurs when the boiler performs a safety check and notices that the temperature sensors for the water going out and coming back are giving conflicting or illogical readings. The most common reason is that one of the sensors has developed a fault or is starting to wear out, preventing the boiler from accurately monitoring its own performance. It pauses the heating process to ensure it doesn't overheat or run inefficiently based on incorrect data.

DIY fix possible

Wait for 15-30 minutes to see if the status clears automatically after the self-test finishesSwitch the boiler off at the fused spur switch, wait 30 seconds, and switch it back onPress the 'Reset' button (indicated by a flame with a line through it) for five seconds

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Related fault codes

F.23View →F.24View →S.97View →

All 170 fault codes on the ecoTEC Plus 635

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

con d.00 D.000 d.01 d.02 d.04 d.05 d.06 d.07 d.08 d.09 d.10 d.11 d.13 d.14 d.15 d.16 d.17 d.18 d.19 d.20 d.21 d.22 d.23 d.24 d.25 d.27 d.28 d.31 d.33 d.34 d.35 d.36 d.39 d.40 d.41 d.43 d.45 d.47 d.50 d.51 d.58 d.60 d.61 d.62 d.64 d.65 d.66 d.67 d.68 d.69 d.70 F.00 F.0 F.01 F.1 F.10 F.11 F.12 F.13 F.20 F.22 F.23 F.24 F.25 F.27 F.28 F.29 F.32 F.33 F.49 F.61 F.62 F.63 F.64 F.65 F.67 F.68 F.70 F.71 F.72 F.73 F.74 F.75 F.76 F.77 F.78 F.83 F.84 F.85 F.86 F.87 F.88 F.89 F.91 F.92 F.97 F22 F70 P.00 P.0 P.01 P.1 P.02 P.2 P.3 P.4 P.5 P.06 P.6 P.07 S.0 S.01 S.1 S.02 S.2 S.03 S.3 S.04 S.4 S.05 S.5 S.06 S.6 S.07 S.7 S.08 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.33 S.34 S.36 S.39 S.41 S.42 S.46 S.53 S.54 S.88 S.91 S.96 S.97 S.99 S.108 S.109 T.02 T.03 T.04 T.05 T.06 T.08

Your boiler is temporarily paused because it has detected a potential issue with its internal sensors while performing a self-test.

What the manual says

What causes this fault?

DIY fix possible

Avoid the next call-out bill

Related fault codes

All 170 fault codes on the ecoTEC Plus 635

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