Valiant ecoTec 418 problem

[Ben_Fisher]

Hi, i have a question about a Valiant ecoTech plus 418 Heat only boiler. the boiler fires up fine but after only 10-15 secs the burner modulate to low and the boiler only manages to get to 50-54oC over the course of the day even with the boiler stat being set to 70oC. the system itself is very clean as it has been flushed, pump seems to be ok and there are no fault codes coming up on the boiler. Any ideas?
Thank you
Ben

 

[Dotty]

Yep. read the forum rules then call a gsr.