I have a propane system mystery, and I am hoping that there is a propane guru out there that can help solve it. We have propane range and heater on our boat, and once lit both function well. Our mystery is: when we have not used the range for a week or longer, it takes a long time to light. I turn on the solenoid valve, turn on the range burner valve and hold a lit match to it, but it may take 30 or 40 seconds (and several matches) to light. "Something" is coming out of the burner all this time, I can hear it and it will even blow the match out if I am not careful, but it is apparently non-flammable and has no odor of propane. After this 30 or 40 seconds, the burner lights, and all is well. If we are using the boat for the weekend once we go through this initial light up ritual, the burners light quickly for the rest of the weekend. Once we leave the boat for a week or two, the slow light up happens again. The propane heater always lights off with no problem, so it makes me think it may be something wrong with the range (all 3 stove burners do it, as does the oven burner). I have leak checked the system with soap bubbles several times, and with the pressure gage at the tank and have found no evidence of a leak. We also have a Trident propane leak detection system aboard that has not indicated propane leakage. I even replaced the propane regulator, thinking it may be the culprit. We have owned the boat for over six years and this mystery has been more of an annoyance than a problem, but I would really like to find out what is causing it. So, has anyone out there had and solved a similar mystery?
Assuming you have properly pressure tested your propane system, what you describe does not sound very mysterious or worrisome to me.
A propane line will often lose much of its content over a period of a few weeks. If there is no detectable leak in the system, that loss is from hose "permeability".
ABYC mandates the UL standard for LP hose permeability for marine installations of propane appliances. Those standards allow for a certain degree of hose permeability. The amount of gas lost through permeability poses no risk during normal operation, but will eventually drain a run of propane hose of some or all of it's contents over a period of time. This is yet another reason (the foremost being true leaks) why it is important to always turn off your propane system either via a remote solenoid valve or at the manual tank valve.
The loss of propane to hose permeability increases at higher temperatures. You'll probably notice it more in summer than in the early or late ends of the season. Also, it's more noticeable on longer propane appliance lines for the simple reason that it takes longer for new gas from the tank to refill the line and reach your appliance when the valve is opened again.
One other suggestion: If you suspect a leak in your propane system, you start by pressure testing it. There is no need to leak check "with soap bubbles" or other fluid unless you've already determined that a leak exists via the pressure test.
To pressure test, you open the tank valve and pressurize the entire propane system (all appliance should be off). Then you close the tank valve (leaving the remote solenoid open or "on"). Record the psi reading on the pressure gauge. Wait 15-20 minutes. The pressure reading should remain constant or not drop more than a few psi. If the pressure holds fine, you do not have a leak, and there is no need to test connections with bubbles.
Note: The pressure test is conducted in a 15-20 minute time period. Not overnight. Not over 3-4 hours. Most systems will lose or gain pressure due to permeability and environmental changes (ambient temp swings) over longer periods. It's conceivable that you could have a slow leak, but not detect it, if temperature increases substantially over a period of time and causes the pressure to increase. Likewise, a big temp drop can cause pressure to decrease, giving the false impression of a leak.