1) Confirm that your condensate pipe is frozen, check for the white looking pipe underneath your boiler this is usually the condensate pipe which leads out to the external wall or quite possibly underneath the kitchen sink.
Check for any fault code or that may indicate blocked condensate pipe.
Listen for any gurgling or bubbling sounds from the actual boiler.
Faults like the above are usually signs that your condensate pipe or boiler maybe blocked with debris
2) Locate the condensate pipe in picture 1 above, place a bucket to catch the condensate water which can sometimes be backed up the boiler or can be frozen at the nearest exposed point.
Use your hands to feel the condensate pipe checking for colder spots this can help you identify the blockage.
DO NOT USE BOILING WATER RISK OF PIPE CRACKING.
3) Pour some warm kettle water into a squeeze bottle, and gently pour some warm water down into into the condensate connection