Low
d4 on Alpha E-Tec NXS

Your boiler is signalling that the temperature setting for your radiators is currently being adjusted or is not being correctly detected.

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

Central heating set point temperature

From this model's manual
Verified against the Alpha E Tec Nxs installation & service manual, page 33.
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 external thermostat or boiler controller to ensure the desired temperature is set correctly.Restart the boiler by turning it off at the wall or fuse spur for 30 seconds and then switching it back on.Verify that all radiator valves are fully open to allow the system to reach the requested temperature.

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

Avoid the next call-out bill

Monthly cover means no unexpected bills when your boiler breaks down.

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

d1View →d5View →

Related guides you might find useful

Radiators cold at the bottom

Sludge build-up — needs flushing, not bleeding.

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 →