Low
S.31 on Vaillant Atmomax

Your boiler is currently set to summer mode, which means it will provide hot water but is intentionally ignoring requests to turn on your central heating.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

No heat demand summer operating mode

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.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

DIY fix possible

Locate the heating temperature control knob on the front of the boilerTurn the knob clockwise away from the 'Sun' icon or leftmost positionCheck that your external room thermostat or timer is set to 'On' and calling for heat

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like S.31: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Related fault codes

S.34View →S.30View →

Related guides you might find useful

No hot water but heating works

Almost always a stuck diverter valve on combis.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →