You may have an RFI (radi frequency interference) problem. Alarm systems and sensors are known to trip when a high power radio
transmitter is being used right up close to them. That could mean you need RFI supression near the propane sensor (sometimes a simple capacitor will do, other times a ferrite bead or choke is needed, neither is expensive) to stop a false trip.
But, if your diagnostics say the sensor is bad, it is time to replace it anyway. If the problem continues, add the RFI suppression.
You are blowing the 15A breaker quite simply because the radio
has been improperly installed. According to Icom:
"Power Supply Requirement: 13.6 V DC +/-15%
Drain (at 13.6 V DC): Transmit (max. output power) 30 A"
That radio requires a dedicated 40Amp fuse or breaker direct to the batteries. Note that it DRAWS 30A which means it will blow a 30A fuse in very little time. It may not blow a 30A breaker as quickly--but it will eventually destroy one by "teasing" it at the full rating.
The RFI problem may also indicate that you have an SWR problem and inadequate grounding (or counterpoise). If you have an autotuner it may be installed incorrectly, that can cause RFI problems while hiding poor SWR. Since the power to the radio was improperly fused/installed, I would expect to find other basic problems like that. (It isn't all quite plug-n-play, not if you want it to really work right.<G>)
Also note that Icom expects the radio to work on 13.6VDC and they really mean 13.6, not 12V. Their radios often suffer performance problems with low voltage, and that means you really need a DC-to-DC converter (a "buck boost") to ensure the radio sees 13.6-14.4 volts when the alternator
is not running.
Of course operating at reduced transmit power will also help avoid the problems, but that's not fixing anything, sometimes you'll want or need full power.
As Rick notes, you should be using heavy battery cables
directly to the radio. You will find online calculators that tell you what cable size to use based on the number of feet (round trip, not one way!) to the battery. For instance, if the power cables
need to be routed 25' to the battery, that's 50' round trip. For a 30A power drain and a voltage drop of 3% (reducing a typical 12.4V to an unstable 12.0 volts which your radio will NOT be happy with) you'd need something between a 4AWG and 2AWG battery cable. (Heavier for welding cable, no savings there.)
Another good reason to compromise (i.e. with 4AWG cable) and install a dc-to-dc converter right at the radio, so the line losses won't affect getting full power to the radio and you won't need wrist-thick cables to feed it.<G> Powerstream is one company that makes these converters, not terribly expensive ($150?).
That voltage drop in the cable can be critical for stable performance from battery power, and will affect your output even when running with the alternator
. Your entire problem with the propane sensor *might* be from RFI because the radio is not getting enough voltage to operate properly. (It should only be that easy.<G>)