The relief pressure is not likely the current setting, it is a point where, no matter where you've got it set, it will limit. Go to one of the big box stores or a local hardware or plumbing supply store and pick up a gauge. You can get one that will screw onto the hose connection at the washing machine, hot water heater drain, or outside faucet for about $10. Use it to check your pressure. THe prv is adjustable and is probably already set at somewhere around 60 pounds or so.
Note, with the PRV and a system that can't handle pressure...you probably want to consider several things. First, if you don't have an expansion tank before the hot water heater, put one in. THen, consider seeing if you can find a T&P valve for the WHeater that will vent at lower than normal. Both will help keep pressure in check.