Low
S.0 on Vaillant ecoTEC plus 612 R1 VU GB 126/3-5

Your boiler is working perfectly; it is simply in standby mode because your heating and hot water are currently at the temperatures you have set.

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 required

From this model's manual
Verified against the Vaillant/Vaillant Ecotec Plus Pro 839592 05 2006 installation & service manual, page 43.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This status appears when your boiler's internal sensors detect that your home has reached the temperature set on your thermostat. Because the target temperature has been met, the boiler physically shuts off the burner to save energy and prevent overheating. It is essentially the boiler taking a nap until the temperature drops and it is needed again.

This code is frequently seen during the summer or shoulder months when your house stays warm enough that the central heating does not need to fire up.

DIY fix possible

Check if your room thermostat is set high enough to call for heatEnsure your programmer or timer is set to 'On' for heating or hot waterWait for the water temperature inside the boiler to drop, at which point the code will change as it starts firing again

Find a Gas Safe engineer
Search the official register →

Avoid the next call-out bill

A cover plan would handle faults like S.0: 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

All 135 fault codes on the ecoTEC plus 612 R1 VU GB 126/3-5

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

Related guides you might find useful