working pressure at boiler

[Agile]

Bster, I dont know why you have had such a problem understanding how to set up the gas valve.

Subject to what the MI say, dis one mod coil wire and set burner pressure to 1.8 mB +/- 0.5 mB.

Reconnect the mod coil and with max DHW load adjust max setting to 13.4 mB +/- 0.5 mB

Whats the problem?

Tony

 

[bster]

how do i i know when gas valve is passing at min rate to allow adjustment in real time with u-gauge.

I am obviously missing something really obvious

 

[ChrisR]

Bster look at the MI fault finding section G, which tells you stuff.
1Volt on mod coil for min gas rate. Quite possibly the same with zero volts - ie disconnected!

Also Mod coil 230mA at 9V so it should be about 9V/0.230A = 39 Ohms, see?

And file the U gauge away for corgi inspections, and get a digi!

 

[bster]

ChrisR - thanks for the resistance thing!

Agile - max output acheived and gas pressure adjusted fine, but the min adjustmnent, going by the MI states that you disconnect one wire, did that and burner would not light, reconnect wire and burner would light - are you saying that i should turn adjustment screw (whilst its not firing) until it does light then quickly note pressure on gauge before max rate is introduced, as i've created the demand for boiler to light from the taps (i know you didnt say any of that but you might of been saying it ).

wishful thinking, good theory or am i talking poppyballs?

 

[Agile]

how do i i know when gas valve is passing at min rate to allow adjustment.

I am obviously missing something really obvious

Yes, you are!

You are missing the fact that with one mod wire disconnected the gas valve is in its minimum setting ready for you to adjust that to 1.8 mB +/- 0.5 mB.

Chris has given you an example of the application of Ohm's Law. That allows you to simply work out the resistance, voltage or current when you know TWO of them.

That example was R = V/A with R in Ohms, V in Volts and A in Amps.

You can fiddle them to find out whatever you want to but probably need a pass in GCSE maths at grades A-C

Using that would have enabled you to decide if a gas valve coil would be 1.5 K or 1.5 M

Tony

 

[bster]

Agile - i did a 1 year GCSE in electronics in 1995 and got a D!!

I'm seriously thinking about doing an evening study electronics course as it is obviously needed for fault finding.



If the mod wire is disconnected - do i set min rate with no demand?

just read section g of MI - so if i get 1v then i know that boiler is at min rate- is this reading taken from connected mod wire and any known neutral?

even more confused now

 

[Rob]

no a genuine 2 mb should be ok, but a U guage isnt as acurate down to the 0.5mbs, so its possible that too lower pressure wouldnt be enough to stay alight, common problem when the boiler trys to modulate but goes out intead

WHAT friking planet are you on bonny lad if yer cant read 1/2 a mill on yer guage either change the gauge or yor glasses

i meant 0.2 as bster was talking about a burner pressure of 1.8

 

[Agile]

Bster, I dont know why you have such difficulty understanding the if the burner goes out with a mod wire dis then the min setting is too low?

Dis a mod wire and with a demand for heat, DHW tap on, adjust the min setting until the burner comes on ( resetting any lockouts on the way ) and then fine tune it to 1.8 mB.

AS far as I can find out a GCSE grade A-C is equivalent to an "O" level grade D-E. Is there any web site which gives all those details?

Tony

 

[ChrisR]

No, measure the mod coil voltage directly across the mod coil (or whatever connector it goes to). One end may be at earth/neutral but it might not be! The mans is AC, this is DC, so is generated on the board and could be isolated from the AC altogether.

I don't think you need to do any electronics course to mend boilers!
If you can work out Speed = Distance/ Time you can do Resistance = Volts/Amps, and Watts = Volts x Amps. That's about it really.
It might be useful to be aware that a coil, like a solenoid or a fan, makes more of a resistance to AC than your meter will read. Can't think of anything else!

 

[bster]

Agile - i understand knowthat if it wont light with one mod wire then the min is too low, but how do you check for the min with burner firing on DHW when it will max out in 10sec's. or do you set, turn water off (zeroing the gauge) turn DHW back on to check pressure (in the 10 sec's before it max's out) if its wrong turn DHW off , adjust min rate , turn DHW on, check initial (min rate) start up etc etc etc etc etc...................

 

[Rob]

Agile - i understand knowthat if it wont light with one mod wire then the min is too low, but how do you check for the min with burner firing on DHW when it will max out in 10sec's. or do you set, turn water off (zeroing the gauge) turn DHW back on to check pressure (in the 10 sec's before it max's out) if its wrong turn DHW off , adjust min rate , turn DHW on, check initial (min rate) start up etc etc etc etc etc...................

as agile said, disconnect one wire on mod coil. the boiler can never fire to full rate in 10 seconds or any time!
if it fails to light as your adjusting the pressure then simply reset till boiler does fire, then adjust to 1.8!

 

[bster]

so if one wire is connected and it lights it is always at min rate?

 

[Agile]

You decide which way to turn the min setting to increase the gas pressure and turn it that way by several turns ! If you dont know then turn it clockwise to increase.

When you get a pressure to measure you can turn it back to 1.8 mB.

Normally, always set the min with the mod coil disconnected.

There are a few models, particularly some Vokera and I think an early Savio which operate backwards.

Tony

 

[bster]

I am really really stupid or just stupid



are you saying that if its firing and i just adjust the min rate (with DHW demand) even though its, say at max output at 13mb, that i dial it down to my 1.8mb and thats it ..min rate set??

 

[Agile]

You are ( probably ) not really stupid, just inexperienced!

Exactly what you have ( at last ) stated.

I once went to a warrantee job where the boiler was not modulating.

It was not surprising! The fitter had set it so the min was at the max, both 11 mB !

Tony