Low
d.08 on Heatline Vizo 24

This code is simply an indicator showing that your room thermostat is currently sending a signal to the boiler to request 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

Current state of the 230V room thermostat

From this model's manual
Verified against the Heatline Capriz Plus installation & service manual, page 25.
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

Check your wall-mounted room thermostat settings to ensure it is set to your desired temperature.If the boiler is running when you do not want it to, lower the temperature setting on your thermostat.If the code persists when the heating is turned off, consult your thermostat manual to ensure it is wired and communicating correctly.

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 d.08: 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 guides you might find useful

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →