Hubby installed a tankless water heater two days ago. He is now gone for a month. When I tried to get hot water I got error code e-2. Upon contacting my hubby he said it’s a code for too much propane gas pressure. He wants me to have neighbor put regulator in line from propane tank and house. is this dangerous to use in the meantime? Btw-I can only get hot water by shutting if off, turning a hot water valve on and turning the gas valve to 1/2 to 3/4 full. I'm worried too much pressure might cause explosion? Thoughts?

Do not operate the unit until the problem is fixed. If you have insurance then you might think about having a professional come out and install a fuel regulator. Otherwise you risk denial of payment if the house burns down.