Gerard,
Did it shoot up with the pump running or drift up over several minutes?
 The hydraulic pressure is very sensitive to system temperature changes.
 Cooling the system can cause sufficient loss to required a recharge by
the pump.  Conversely when heated, temperatures can cause the pressure
to bump up against the relief valve.  I have had  a cylinder at 2000+
plus with no ill effect.  The hydraulic test rig was close to the hangar
door with a single cylinder pressurized to 1200 psi and isolated from
the pump.  The sun swung around at warmed the cylinder.  The next glance
at the pressure gauge showed it on the stop at 2000+ psi.
I wouldn't worry too much about 1700psi.  If it goes higher you might
want to adjust the relief valve down a bit.  To test the actual relief
valve setting, force the pump on for a second or two after the pressure
switch has turned the system off.   Your gauge will tell you what
setting you have.  If you do make adjustments keep in mind that the
relief valve setting must remain higher than the pressure switch setting
by some margin.
Chris Zavatson
N91CZ
360-std
900 hrs