3 1 Low

Grant 3 1 Fault Code

Also written as 31 — same fault.

The Grant 3 1 fault code means: your boiler has detected that the water inside the system is soft, meaning it contains very low levels of limescale.. It appears on 1 Grant model in our database.

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.

Technical description: Soft <70 mg/l calcium carbonate

Engineer required

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

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like 3 1: 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.

Grant models that show the 3 1 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Grant 3 1 fault code information on this page is sourced and cross-checked against the official Grant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026