28i Junior modulating in minimum mode

[Nat]

Hi all,

Was wondering if anyone had come across this before or might know what the problem is.

Trying to adjust the air gas ratio on a 28i junior. Put it in service mode. Turn the dial to maximum. Boiler goes to full output. Adjust the valve to get the reading I need. All good. Then turn down to minimum and the boiler won't stop modulating up and down so impossible to get a reading to adjust the gas valve.

Anyone got any ideas?

Many thanks,

Nat

 

[Dotty]

Moved to GSR only forum.

 

[zeebeedee]

Got be a stat/pcb fault. That would be my first port of call

 

[vern]

Hi all,

Was wondering if anyone had come across this before or might know what the problem is.

Trying to adjust the air gas ratio on a 28i junior. Put it in service mode. Turn the dial to maximum. Boiler goes to full output. Adjust the valve to get the reading I need. All good. Then turn down to minimum and the boiler won't stop modulating up and down so impossible to get a reading to adjust the gas valve.

Anyone got any ideas?

Many thanks,

Nat

what readings you getting on low? From to etc? What gas valve prettle or sit?

 

[villa_tom]

The gas valve may be so out of range its modulating because if that. I had one once that I could not get a reading off.

The best way to get there is to turn the boiler off and wind down the gas valve on high and low and adjust it that way.

When you first fire up the boiler it won't light until you start adjusting it.

Failing this I'd say its probably something pcb related, or electrical related atleast.

 

[arran197]

When you say modulating, is the fan speed going fast then slow or is the boiler cutting off, then firing back up? May well be that the gas valve after setting the high up, is now out of adjustment on low so much that it won't remain alight on minimum. If you call Worcester, they should give you the instructions on how to 'reset' the gas valve back to it's factory settings. You can then start all over again with the adjustment.

If the fan speed is going fast and slow, could be the fan is about to completely go. My guessing would be the gas valve adjustment though.

 

[villa_tom]

Here are the factory set gas valve settings that worcester will tell you. Print this off and use this, save on expensive phone calls to worcester
p

 

[villa_tom]

The above post is for a sit gas valve, but I found those more common anyway

 

[SafeGasInstall]

you need to start from low flame

when you say modulating I am sure boiler does not fire and then fun clears burning chamber

put boiler on ch and turn thrmostat on 2 and then keep analyser in and adjust when stable and happy put to service and do the same
and after pls recheck low flame again just to be 100% sure

 

[Nostrum]

Yes agree with above, sounds like the gas valve had been incorrectly adjusted. My bet is the 4mm has been adjusted on max, then the boiler won't stay lit on minimum so ramps up to fire, then drops down, goes out, repeat etc.

9 times out of 10 you can turn the 4mm clockwise 1 full turn and it will be enough to stay lit and go from there.

allways adjust max first as its does have an effect on min settings, whereas min (4mm) does not have an effect on max once set.

 

[Atouchofgas]

If I remember correctly if you screw high/low right in the back 7 turns it should get you in the ball park figure

 

[Derek Hardman]

If it is a Prettle gas valve it will never be happy, change it for a sit valve, you can get a replacement kit which comes with instructions because some of the connected parts have to come out, its easy enough to do though.