Loud Thump when Boiler First Ignites Only

[lev]

Hi everyone.
Please can you help. Everytime the boiler ignites i.e. first time in the morning and first time in the evening, there is a very large and instantaneous loud THUMP rattles round the pipes . It only happens on first ignition when all the pipes are cold. If I manually stop and start the boiler either CH / HW its fine. Its a wall mounted IDEAL boiler in a Y plan config.
Thanks in advance . N

 

[ChrisR]

Has it been serviced this century? (Most haven't!) Could be pilot too small - which Ideal boiler?

 

[lev]

Thanks for quick response.

Yeah it was only fitted last year, its an IDEAL Class RS 360

N.

 

[BDL]

Best get it serviced, could be burner pressure or debris in burner. There is an upgrade for the Classic Rs range to overcome flame lift problems, how old is the boiler?

 

[lev]

Hello

Its probably about a year old. Its strange that it only happens once or twice a day after it has not been on for a while, like overnight, or through the day, and not every time it ignites.

n.