Worcester blocked condensate trap
On the early Worcester Greenstar range the Junior and Si(and Ri) had a condensate trap. The condensate traps job is to safely collect and release the condensation created by a condensing boiler. On later Junior and Si models this was upgraded to a better type of trap which Worcester likes to refer to as a Siphon.
All condensing boilers require a condensate trap of some sort, some are better designed than others. On the early Junior/Si the condensate trap was susceptible to blockages. The Ri also has a condensate trap but doesn’t really suffer from the same issues as the Junior/Si.
A blocked condensate trap is not the most common issue on the early Greenstar range but it is a problem. The problem is caused by the trap being blocked by small particles of aluminium. The primary heat exchanger on the Greenstar range is made from aluminium. The condensation created by a condensing boiler is slightly acidic and corrosive. Over time tiny bits of the heat exchanger are corroded and make their way into the sump and into the condensate trap.
Once the bits of aluminium block the inlet tube on the trap then it will stop the flow and the condensation will keep backing up into the bottom of the heat exchanger until it stops the appliance from breathing and suffocates it. This will stop the appliance from working altogether.
If your appliance is regularly serviced PROPERLY by someone suitable who does a good job, which includes cleaning the primary heat exchanger or the condensate trap at least, then this will probably never cause an issue.
I tend to come across this problem on appliances that haven’t been serviced properly or at all for some time. The upgraded siphon on later models is a big improvement and doesn’t tend to suffer from this issue as much but still needs cleaning from time to time.
Symptoms of this issue will include a slight gurgling noise from the boiler, also if you go outside and listen to the flue it will be make an unusual sound. The boiler will attempt to light its burner but fail and go to ignition lockout.