Potterton Fault Code E133 Repair
E133
– Failure to light (could be a gas supply issue). Check that the gas supply is available. If possible try lighting a gas cooker or fire
Intro
By definition of the manual this is mostly to do with ignition. However there can be a range of possible causes from gas components to electrical components. The time of year this fault occurs also has high relevance. If this fault is occurring during extremely cold weather, then it is very likely that you have a blocked or frozen condensate.
Frozen Condensate
To defrost the condensate pipe,switch off boiler, get hot water (approximately 50 degrees would be considered adequate), and pour on the exposed pipe until it is clear. Switch on boiler and reset if necessary. Repeat the sequence if necessary, otherwise proceed for further diagnostics.
An alternative termporary solution  – would be to cut the condensate pipe internally and place a flexible pipe going into a bucket. Please note a bucket and towels may be required in order to catch the trapped water. If this solution works, then it confirms the condensate pipe is indeed frozen or still blocked.
Normal Weather Conditions
If this error is occurring in normal weather conditions. Then it would be recommended to get the ignition electrodes checked. It’s also possible that the gas valve has failed
There have been reported cases of fault pcbs with this error too. You may need to get the PCB tested and replaced if necessary