High
1 flash green on Potterton Apollo

Your boiler has shut down because the water inside it has become too hot, too quickly, or is not circulating properly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Temperature protection (Maximum flow temperature exceeded, Flow temperature rise rate too high, Excessive difference between flow and return temperature)

From this model's manual
Verified against the Potterton/Potterton Bm Potterton Potterton Ultra System Compressed Pdf installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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 1 flash green: 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.

All 34 fault codes on the Apollo

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

1 flash red2 flashes green2 flashes red3 flashes green3 flashes red4 flashes green4 flashes red5 flashes green5 flashes red6 flashes green6 flashes red15202840110125130133135160E20E28E50E110E119E125E133E160Lights Flash Flash OnLights Flash Off FlashLights Flash Off OnLights On Off Flash

Related guides you might find useful

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →