Worcester Greenstar 30Si service
This is an example of what I generally do when I service a Worcester Greenstar 30Si. This appliance is very similar to the Greenstar Junior with a few differences. A boiler service is first and foremost to check that the appliance is working safely, and will continue to do so for the foreseeable future(the next 12 months). It also involves checking the appliances components which are responsible for keeping the boiler running. So I want to make sure it is working safely and then do whatever is necessary to keep the boiler running sweet until its next service is due. Components which are failing can be pointed out to a customer who ultimately decides if they want to replace them – assuming they don’t affect safety.
Drain the appliance
First of all I drain the appliance. There is a drain off point on the right hydraulic block just underneath the pump. This is where you can see the orange tube connected. The reason I drain the appliance down is so that I can check the pressure inside the expansion vessel. The expansion vessel is a cylinder with a rubber tube inside which regulates the pressure in the system when the heating is on. If the tube goes flat it doesn’t work. The pressure just builds up when the heating is on and get released from the pressure relief valve when the pressure exceeds 3 bar.
This is a very common problem on combi boilers, system boilers and sealed systems. The expansion vessel is a serviceable component and should be checked every 3 years, although I generally do this on every service.
On these boilers the expansion vessel is situated behind the boiler. Most engineers prefer it when the vessel is accessible. This is because sometimes the expansion vessel has to be replaced and if you can’t get to it the job becomes a bit more difficult. Usually the boiler has to be removed from the wall or an external vessel can be fitted. Once the tube has been reinstalled(if neccesary) then I check it with a digital pressure gauge. On most combi boilers the pressure needs to be in the region of 0.8 bar.
After I have taken care of the expansion vessel I remove the fan assembly. On these appliances you have to remove the fan to remove the burner and the spark electrode assembly. To remove the fan you need to remove the connection to the gas valve, electrical connections on the fan and the retaining clip that holds it all together.
Spark electrode assembly
In the images below you can the spark electrode/ionisation probe assembly attached to the re burner gasket. The image on the left shows what the assembly looks like after the boiler has been in use for some time. On the right is what they look like after cleaning. I usually use a combination of a wire brush and fine sandpaper to clean these. If left without being cleaned long enough these electrodes will stop working eventually which is the reason why I do this on a service.
On some appliances burner are prone to failing. Sometimes they need to be cleaned. The Worcester Greenstar’s don’t seem to suffer from either of those but I generally remove the burner just to make sure it hasn’t imploded(this does happen on some appliances), then I replace it. The image to the right shows the red burner gasket when it fails. This gasket failure is not uncommon on the Junior and Si which basically makes the appliance unsafe when it happens, hence I like to check these and replace if necessary. I carry this gasket as stock, they cost about £10.
Once the previous checks have been done I replace the burner, gasket, electrode assembly and fan. After that I refill the system to about 2 bar. I overfill the system as the heat exchanger has to be bled of air. If you don’t do this it can cause the heat exchanger to overheat and result in a callback. There is a valve with a tube at the top of the heat exchanger for this purpose. This is done until the appliance gets back down to 1 bar. I also bleed the pump of air at the same time, this has its own bleed screw. This is a condensing appliance which means it has a condensate trap. The image below on the right shows this. The condensate trap can be removed and cleaned but is not always necessary. Its important to check these for leaks though as the condensation produced is corrosive. The appliance is also checked over for leaks. A common point for boilers to leak from is the auto air vent, which is usually located at the back of the pump.
‘FAGS’ stands for Flue, Air, Gas and safety(device).
Once the boiler has been put back together and filled up with water it is time to test it.
Each appliance has a specification and one of the checks involves checking to see how much gas the appliance is using.
The flue gasses are also analysed with a flue gas analyser. This tells you how efficient the appliance is, how hot the flue gasses are and how much CO etc the appliance is producing. This has to be within a certain tolerance.
The safety device on the appliance is tested by turning off the gas. The boiler should try to reignite itself and go to a lockout state within 3 attempts of ignition.
The flue integrity and termination point are also checked as well as the air supply. Modern domestic boilers are usually ‘room sealed’. This means their air supply from outside and expel the flue gasses outside as well. They are only room sealed when the case seals that seal the main combustion cover are intact, so this is checked as well.