This is the first mention of propane as the fuel- I had assumed you were on the gas grid. I don't have much to offer on your valve/pressure flucutation enigma, but I DO have a suggestion on a cheaper/better way to heat at least part of the house.
At CT-style propane & electricity prices heating with a better-class ductless air source heat pump would have about 1/3 the cost of heating with condensing propane. With any reasonably open floor plan you should be able to heat/cool at least one of your zones with a single ductless head (a 1-head mini-split), and you maybe able to do both reasonably with a one-head per floor approach. Though that works better for high-R houses, even if it's only covering your average winter load you'd be able to cut your propane use by more than 3/4, making it self-funding in short years on propane savings. A pretty-good high efficiency 1-ton like the Fujistu AOU 12RLS2 (or 12RLS2-H) would run about $3.5-4K (installed) and can deliver about 17,000BTU/hr @ +5F, more at higher temps. A 1.5 ton Mitsubishi MSZ-FE18NA puts out over 22,000 BTU/hr @ +5F and runs $4-4.5K installed.
Getting a handle on your room by room and whole house heat load would be necessary to size it correctly and pick a model that works, but it's almost a no-brainer type investment if you intend to stay there more than 3 years. For the broader picture, download and ponderthis short policy piece from last March. If you need or want climate specific performance information I can point you can get pretty deep into the weeds on it on the NEEA field metered test data. In a coastal CT climate they are nearly as efficient as ground source heat pumps if you get a decent one.
At CT-style propane & electricity prices heating with a better-class ductless air source heat pump would have about 1/3 the cost of heating with condensing propane. With any reasonably open floor plan you should be able to heat/cool at least one of your zones with a single ductless head (a 1-head mini-split), and you maybe able to do both reasonably with a one-head per floor approach. Though that works better for high-R houses, even if it's only covering your average winter load you'd be able to cut your propane use by more than 3/4, making it self-funding in short years on propane savings. A pretty-good high efficiency 1-ton like the Fujistu AOU 12RLS2 (or 12RLS2-H) would run about $3.5-4K (installed) and can deliver about 17,000BTU/hr @ +5F, more at higher temps. A 1.5 ton Mitsubishi MSZ-FE18NA puts out over 22,000 BTU/hr @ +5F and runs $4-4.5K installed.
Getting a handle on your room by room and whole house heat load would be necessary to size it correctly and pick a model that works, but it's almost a no-brainer type investment if you intend to stay there more than 3 years. For the broader picture, download and ponderthis short policy piece from last March. If you need or want climate specific performance information I can point you can get pretty deep into the weeds on it on the NEEA field metered test data. In a coastal CT climate they are nearly as efficient as ground source heat pumps if you get a decent one.