No modulation on burner

[tabs]

Glowworm swiftflow 100. There is no modulation on the burner. As a consequence on the CH side the pressure is shooting up to over 3 bar as the boiler overheats and the gas valve shuts off.

Will it be the modureg or some electrical fault?

 

[geoff@cetltd]

Well, if you measured the volts coming out of the pcb, you'd be able to answer this yourself, wouldn't you

 

[Agile]

It could also be that the gas valve is way out of adjustment!

This would only normally happen if some incompetent person has been fiddling with it though.

Tony

 

[tabs]

Well thanks for your help Raden - so generous.


Tha pcb has already been replaced , so what I'm basically asking is could there be an electrical fault somewhere else causing this, such as the from the user control pcb or anything else?

 

[Rob]

so what I'm basically asking is could there be an electrical fault somewhere else causing this, such as the from the user control pcb or anything else?

yes along with many other things. have you or your engineer managed to measure min and max gas pressures?

 

[tabs]

The burner pressure stays at 5 mbar for both DHW and CH.

 

[corgigazza]

If you read the instructions you will see that you can adjust the pcb out put for ch using a small flat screw driver then adjust the correct potentimometer to suit

 

[tabs]

Yeah - I've already tried that with the u gauge on - no change at all to the burner pressure. For some reason the gas valve only opens upto 5mbar.

 

[geoff@cetltd]

Well thanks for your help Raden - so generous.

Tha pcb has already been replaced , so what I'm basically asking is could there be an electrical fault somewhere else causing this, such as the from the user control pcb or anything else?

I didn't ask if the pcb had been repaced

I said did you check the modureg voltage from the PCB ?

 

[Agile]

The gas valve has minimum and maximum setting which have to be adjusted by a competent person who would usually be CORGI registered.

Until the gas valve setup has been confirmed as correct there is little point in considering any other option.

There is also an assumption above that fitting a new PCB will have eliminated all faults associated with the PCB. There is always a possibility that the new one was faulty as supplied, damaged during ijnstallation or wrongly adjusted on installation.

Tony

 

[tabs]

Agile - I take your point the pcb could still be faulty.

However ,how would you set the min and max pressures though when the burner is either on or off at the moment with nothing in between even when the potentionmeters are adjusted.

Sorry if I'm being a bit dumg here.

 

[Agile]

If the minimum setting equals the maximum setting then there is only one burner pressure. I often come across that when the gas valve has been tampered with.

The normal setup involves setting either minimum or maximum first and then setting the other parameter. Only after the gas valve has been set up correctly can the PCB settings be adjusted.

Unless I had confirmation that you were CORGI registered then I cannot give precise details of the setting procedure in this particular case.

Tony

 

[tabs]

Thanks for your response agile . Sorry I can't give confirmation I'm CORGI registered as I'm not yet. I take my ACS in 2 weeks and will then seek registration with CORGI unless some other registering body is available then

OH and it is my own boiler.

 

[Paul Barker]

The burner pressure stays at 5 mbar for both DHW and CH.

The correct max pressure is 16.3mBar and minimum 1.5. Are you sure you are reading the guage correctly?

Since you are part way qualified it is your boiler and you have a u guage.

Are you puting u guage on correct part of gas valve, remember working pressure and standing pressure are taken from test point nearest incoming, operating pressure sometimes called burner pressure from test point furthest from incoming on most boiler gas valves.

Tests are usually only possible on hot water mode. Max pressure is confirmed by running bath and basin taps full on, should be 16.3. Min pressure is confirmed by removing one lead of coil on gas valve.

Adjustment is outer nut for max, inner screw for min. Must hold opposite one still while adjusting and recheck one after adjustment of other. Fine tuning via pcb pot on that boiler, but you are far from fine tuning.

I don't know the voltages that this gas valve works on, but set meter on dc volts 250 range. Test at correct two pins of pcb or at end of leed to gas valve. You'd expect changing voltage as you run a tap slow or fast.

By the way, there is a dhw high limit stat so I am conscernmed about the 3 bar pressure, the high limit stat should prevent rediculous levels. I suspect there is also a problem with the expansion vessel. Take off the dust cap depress the pin, if water comes out you need a new one, if air, you need to check the charge pressure, and pump up as required.

I don't know what the performance of this pcb is when an ntc (negative temp coefficient) thermister (resister that varies with temperature) is out of range some won't procced to anything, this one may act bisaarly as your seems to. You need to obtain the temperature resistance chart for the ntc, ask the manufacturer explain your level they may provide it. First and most simply we check the room temperature resistance, if it fails this we change it anyway. Probably the same part for CH side so we swap them over in the first instance to fault fine. Full test involves jug of water thermometer and ohm meter. For most boilers its a very cheap part so we don't quibble and change it anyway. Halstead's it costs £25 so we think twice, but I bet there is an Ariston part which is right.

 

[Paul Barker]

I'm now going to put my corgi manual down my trousers ready for a smack for giving too much information.