No Options Apply Suburban hotwater unit wont run unless door is open.

[Sparksy]

Been away for past 3 weeks, some of which was offgrid. When running the hot water on gas i have a issue where the Suburban hot water unit will only run with the door slightly ajar. If closed the sound of the flame drops from normal "roar" to a softer sound and eventually the flame fails. Door vents are clear, flame tube is clear , flame rods are bright and as far as gas pressure goes, all 3 burners look fine when running at once.
Managed to use it on gas by tying the door open about 15mm with a bit of wire between catch and door.
Has anyone encountered this before?

 

[Drover]

Yes.................. someone had a thread going not that long ago, wish I could remember the cause, Im sure we discovered why.................

 

[jazzeddie1234]

Twas me! The flame is supposed to create a small current flow across the probes that is detected by the circuit board and that holds the gas solenoid open....until the board develops a fault and is not sensitive enough. The board is expensive so I just open the door each time I use gas.

PS don't try bending the probes as they will snap....don't ask me how I know this

 

[Sparksy]

Ive cleaned the probes but if it was the board then the board would instantly switch off the gas. In this case the flame slowly looses intensity ( for want of a better word) and slowly reduces over about 2 minutes. If I didnt know that the vents were all clear, I would swear that it was because of a sealed enclosure and the flame using up all the air in there but of course it isnt. Ill try swapping over the board and probe as I have new spares at home.

 

[Drover]

Many moons ago I had a drama with a HWS , would start up but would stay on for a few minutes or just shut down once the start time had elapsed, turned out the thermocouple had a bad connector and the poor signal would shut down the gas solenoid .. did lots of testing with the meter before I found it .....

If it works with door open then I doubt its the board does sound like the door closed may be distorting the frame and movinig the thermocouple just a mm away from the flame so it not getting the right temp and shuts the gas off, just can't see how it could starve the air flow though and the gas should shut off instantly ....

 

[jazzeddie1234]

It could be the probes but the board has a well documented fault where the sensitivity to the flame (well the current measured as the flame passes the probes) is well documented on older boards anyway. I tried cleaning the probes, bending them in and out of the flame, changing the air gate (looks like a hose clamp), adding an extra vent grill to the door....

Definitely interested in what you find!

 

[Drover]

Ive cleaned the probes but if it was the board then the board would instantly switch off the gas. In this case the flame slowly looses intensity ( for want of a better word) and slowly reduces over about 2 minutes.

I think thats the clue, the flame is either on at full noise or totally out, it doesn't vary as it doesn't have a pilot, its sparks and start ................ To me slowly dying would point to a faulty solenoid thats closing slowly instead of instant shut off or starving of air as you said but its not like the door seals off anything and how would closing the door effect the circuit board, its a most intruiging problem ..................... possibly a combination of faults ................. I too await the outcome .......

 

[Boots in Action]

Many moons ago I had a drama with a HWS , would start up but would stay on for a few minutes or just shut down once the start time had elapsed, turned out the thermocouple had a bad connector and the poor signal would shut down the gas solenoid .. did lots of testing with the meter before I found it .....

If it works with door open then I doubt its the board does sound like the door closed may be distorting the frame and movinig the thermocouple just a mm away from the flame so it not getting the right temp and shuts the gas off, just can't see how it could starve the air flow though and the gas should shut off instantly ....

I had a similar problem regarding the thermocouple with my 3 way fridge. All was fine for months and then when I was testing fridge at home, found that fridge would light and run for about 15 minutes and then flame would go out and fridge would stop working. After a normal restart some minutes later, same thing would happen again!! As each successive restart happened, running time would reduce before failing. When it got down to under 5 minutes, I realised there was a real reliability problem. Cleaned the flame end of thermocouple, checked positioning in flame and then changed the thermocouple but still failed to continue to run. Then also changed the little cutout connector at back of gas control switch where end of thermocouple joined, and also upgraded the thin light wiring to really heavy stuff for the flame indicator. Result . No more gas flame going out and flame indicator now sits at end of scale in GREEN instead if just struggling to get from RED zone to GREEN . Obviously the flame indicator is a guide to how much current/voltage is generated within the thermocouple when heated. I think it had something to do with the very small electric current generated by the pilot light when heated, and the slow loss of current/voltage leaking away from the shut off valve until the valve finally closed and shut off the gas entirely. That is how I fixed mine and I have no circuit board or door worry about. I hope this gets the thoughts going on checking how much voltage/current is generated within the thermocouple and where current/voltage is slowly "leaking" away by the time it gets to the cutoff valve. As for the "door thing", I am at a loss to even suggest anything!!!

 

[Sparksy]

Thanks. But the suburban hot water doesnt use a thermocouple to hold the flame failure solenoid for gas flow. I can see your point but the flame detection works by current flowing through the flame from a prob to another probe which is connected to the frame. The control board once the flame starts ignition, has a voltage output to the probe and the board detect current flow through the flame. No flame , no current so solenoid closes.
Ive cleaned the probes and the flame tube and have monitored the voltage on the solenoid valve which remains constant even though flame slowly dies.
Im now waiting for a gas fitter mate to lend me his manometer to see if there is a drop in gas pressure but he doesnt think that is the problem.

 

[Boots in Action]

Thanks. But the suburban hot water doesnt use a thermocouple to hold the flame failure solenoid for gas flow. I can see your point but the flame detection works by current flowing through the flame from a prob to another probe which is connected to the frame. The control board once the flame starts ignition, has a voltage output to the probe and the board detect current flow through the flame. No flame , no current so solenoid closes.
Ive cleaned the probes and the flame tube and have monitored the voltage on the solenoid valve which remains constant even though flame slowly dies.
Im now waiting for a gas fitter mate to lend me his manometer to see if there is a drop in gas pressure but he doesnt think that is the problem.

Thanks @Sparksy for that info and the fact that the Suburban hot water system does NOT use a thermocouple to keep gas valve open. However, it does require a voltage/current source from somewhere and according to your thoughts, this must come from the control board once flame is lit. Perhaps there is a small capacitor that is not holding charge at times, but is allowing voltage to flow through it without maintaining sufficient charging /constant current to maintain a detectable current flow through the flame to other probe, even if VERY VERY small. Another cause could be a combination of voltage/extremely low current unable to maintain a though circuit? and/or poor connection to frame. Ideas now coming out of remote, but possible fields!!

Incidentally, my understanding of the operation of a thermocouple is when two dissimilar metals are heated in a flame, one metal becomes positively charged and the other negatively charged. As the ends away from the flame have a different electrical potential, a small current will flow between them when connected. Current does not actually flow through the flame. I am happy to be corrected if my understanding is incorrect.

 

[jazzeddie1234]

Im now waiting for a gas fitter mate to lend me his manometer to see if there is a drop in gas pressure but he doesnt think that is the problem

A good thing to rule out though. I have heard of a few cases where it was a problem with the regulator