Everyone seems to have ignored this. Incorrectly adjusted gas pressures would not cause this to happen. You have some other fault (CH circulation obstructed?). Perhaps there is nothing wrong with the either PCB or gas valve?tabs said:
No modulation on burner
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I agree it is an issue Paul. Are we going to cause widespread deaths and explosions due to people having a go, not checking the test points aren't leaking, getting it wrong and melting their boilers, burning themselves and the rest? The target of the advice may know enough, or not, but most diy readers won't. (Even if they quote some number to Tony to pretend they're RGI'sPaul Barker said:
)Thanks for the advice Paul. It wsa a good read .This has been a very good learning experience for me . I've just checked the voltages to the modureg . There is 20volts at the modureg so it should give max pressure of 16mb on DHW but it doesn't and there is no modulation of burner as voltage is either 20v or goes to zero if flow of hot water is turned too low. I then disconnected the user control pcb to see if this was interfering with the modulation. Bingo - I managed to get modulation on the DHW- all the way upto 20v and back down again ( I haven't yet tested this with U gauge cos I am ill and cream crackered). Then tested this with the CH but after running it there was no modulation - pressure just carried on increasing with voltage on modureg steady at 20v then valve shut off just as it passed 2 bar.
Having just spoken to my boss about this I think we have concluded the modulation fault lies with a problem on the user control pcb - there must be some feedback to it via the CH thermister which was why there was no modulation on the CH when it was disconnected but was modulation on the DHW.
I am still concerned, as has been mentioned in this thread, about the fact that the pressure has been getting to over 3 bar before the gas valve has shut off so will also check the pressure expansion vessel as suggested.
I'm assuming its the overheat stat that is shutting the gas valve in this case?
Again thanks for all the advice and just to assure folks I'm not claiming I'm a RGI .
PS: My boss is gonna take a quick look at the user control pcb tommorrow , may be just a resister has gone - if not its a new one from parts centre
. I've just checked the voltages to the modureg . There is 20volts at the modureg so it should give max pressure of 16mb on DHW but it doesn't and there is no modulation of burner as voltage is either 20v or goes to zero if flow of hot water is turned too low. I then disconnected the user control pcb to see if this was interfering with the modulation. Bingo - I managed to get modulation on the DHW- all the way upto 20v and back down again ( I haven't yet tested this with U gauge cos I am ill and cream crackered). Then tested this with the CH but after running it there was no modulation - pressure just carried on increasing with voltage on modureg steady at 20v then valve shut off just as it passed 2 bar.Having just spoken to my boss about this I think we have concluded the modulation fault lies with a problem on the user control pcb - there must be some feedback to it via the CH thermister which was why there was no modulation on the CH when it was disconnected but was modulation on the DHW.
I am still concerned, as has been mentioned in this thread, about the fact that the pressure has been getting to over 3 bar before the gas valve has shut off so will also check the pressure expansion vessel as suggested.
I'm assuming its the overheat stat that is shutting the gas valve in this case?
Again thanks for all the advice and just to assure folks I'm not claiming I'm a RGI .
PS: My boss is gonna take a quick look at the user control pcb tommorrow , may be just a resister has gone - if not its a new one from parts centre
No , not the user control pcb
Having meassured the voltage at the modureg -there is 20V there on both CH
and DHW. These voltages do vary if I adjust the potentionmeters on the main pcb but they do not vary as the flow of water is reduced on the DHW or rads are closed off once the system is on CH.
I had a u gauge connected while measuring the voltage at the modureg and even when adjusting the potentiometers and the voltage was varying at the modureg the burner pressure never varied from about 5 mbar.
I have tested both CH and DHW thermistors and both are working. I can't believe the modureg itself has gone. I mean what are the chances of the fan, main pcb and modureg going at the same time?
Help .........please
Having meassured the voltage at the modureg -there is 20V there on both CH
and DHW. These voltages do vary if I adjust the potentionmeters on the main pcb but they do not vary as the flow of water is reduced on the DHW or rads are closed off once the system is on CH.
I had a u gauge connected while measuring the voltage at the modureg and even when adjusting the potentiometers and the voltage was varying at the modureg the burner pressure never varied from about 5 mbar.
I have tested both CH and DHW thermistors and both are working. I can't believe the modureg itself has gone. I mean what are the chances of the fan, main pcb and modureg going at the same time?
Help .........please
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"""I have tested both CH and DHW thermistors and both are working"""
Can you explain what tests you have conducted to determine they are working?
A normal RGI test of modulation is to turn the tap on full and disconnect one mod coil lead and it goes to min gas. I dont see anywhere you have said that?
Tony
Can you explain what tests you have conducted to determine they are working?
A normal RGI test of modulation is to turn the tap on full and disconnect one mod coil lead and it goes to min gas. I dont see anywhere you have said that?
Tony
the fact that you cant get more than 5 mbar yet the pcb is calling for max input suggests the fault lies with either the working pressure or the gas valve.
probably the main solenoid guvenor rather than the modulation solenoid. which is fauly however could it possible that its blocked somewhere?
probably the main solenoid guvenor rather than the modulation solenoid. which is fauly however could it possible that its blocked somewhere?
One way to test ntc's is to buy a new one and hold it under the tap, see if it fixes fault. Usually the primary side ntc has a lot more hammer than the domestic, so even though it is faulty on dhw it is more likely to be the primary ntc. A preset in place of the ntc could be used to check for modulation but dont adjust it too quickly as the pcb knows at what rate to expect a change and will throw a wabbly if you adjust it at the wrong rate. Better to try a new ntc as they are a cheap part and always worth having in stock.
Are you sure someone hasn't partcially closed the ecv at the meter? This is very common. Your cooker might be unaffected and your central heating would work, but you would have poor hot water performance.
Are you sure someone hasn't partcially closed the ecv at the meter? This is very common. Your cooker might be unaffected and your central heating would work, but you would have poor hot water performance.
"""No ECV is fully open , am getting virtually 21 mbar at the boiler gas valve as well."""
I know this is obvious but you would be surprised how many RGIs with 10-20 years experience dont do this properly! The pressure at boiler input MUST be checked with the boiler operating !!!!
The text book is three rings on a cooker but this is only about 5 kW and modern boilers can use 30-40 kW and thats a lot more load for a dogey regulator.
I once went to this RGI who had spent three half days and changer TWO gas valves. He had tested the hob and it was fine. The boiler would not fire up though.
He forgot to measure the gas pressure at the inlet of the boiler WHILE it tried to fire up. Or even leave the hob running when trying the boiler.
I found the fault when I asked the new owner where the gas valve was. He did not know! It was a card meter which had run out but was leaking internally and running the hob but not the increased load of the boiler!
Tony
I know this is obvious but you would be surprised how many RGIs with 10-20 years experience dont do this properly! The pressure at boiler input MUST be checked with the boiler operating !!!!
The text book is three rings on a cooker but this is only about 5 kW and modern boilers can use 30-40 kW and thats a lot more load for a dogey regulator.
I once went to this RGI who had spent three half days and changer TWO gas valves. He had tested the hob and it was fine. The boiler would not fire up though.
He forgot to measure the gas pressure at the inlet of the boiler WHILE it tried to fire up. Or even leave the hob running when trying the boiler.
I found the fault when I asked the new owner where the gas valve was. He did not know! It was a card meter which had run out but was leaking internally and running the hob but not the increased load of the boiler!
Tony
It sounds as if there is an inadequate gas supply as well as a boiler fault.
What you should have measured as well is the gas pressure at the meter so that the pressure loss in the supply to the boiler can be known. Should be under 1 mB !!!
With the boiler fixed and running at full power the working pressure couls be dangerously low.
Tony
What you should have measured as well is the gas pressure at the meter so that the pressure loss in the supply to the boiler can be known. Should be under 1 mB !!!
With the boiler fixed and running at full power the working pressure couls be dangerously low.
Tony
preset is small trimmer pot adjustable using special tool.
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