Common problems guide

The most common Main 12 Heat ErP problems

The faults most likely to send a Main 12 Heat ErP into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

4 documented codes
4 most common
0 DIY-safe checks
4 engineer needed

The 4 most common faults

01
IGNITION LOCKOUT Engineer

Is there gas at gas valve inlet? Is there gas flow from gas valve? Is there at least 18mbar dynamic at gas valve inlet?

Full guide for IGNITION LOCKOUT
02
OVERHEAT LOCKOUT Engineer

Disconnect black stat on flow pipe. Disconnect fan stat. Disconnect the larger of the 6-way PCB connectors. Disconnect thermistor.

Full guide for OVERHEAT LOCKOUT

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Main shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
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.

See the full 4-code list for the Main 12 Heat ErP

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →