Regional Jet 700 ER/LR (CRJ700)
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude
Flight Crew Overcame Equipment Problem
Aircraft
Aircraft on downwind vectors for ILS.  At approx. 3500 MSL Captain's radio alt began fluctuations/readings of 1000' AGL w/ +/- 1500 foot deviations up and down.  Intermittent GPWS 'Terrain' warnings began.  Even though it was an obvious malfunction indication; the flight was in IMC so the escape maneuver was initiated.  The warning stopped during escape almost immediately; followed by more RA fluctuations on CA PFD.  F/O side did not indicate any abnormality or RA issues throughout event.  Flight deviated from ATC clearance (assigned altitude) during maneuver; ATC was advised during climb.  After warnings stopped; altitudes were re-verified to be correct and safe; and approach vectors were continued.As a company we need to be more proactive in fixing GPWS/radar alt. faults; not just 'clearing' the malfunction(s).  This was a repeat write-up that was not troubleshot in any detail according to the maintenance log.  This can create two hazards: 1. False warnings leading to unnecessary go-arounds; etc.; as in this case; and 2. conditioning crews not to take GPWS warnings seriously; as many times the event is dismissed due to repeat write ups.It is necessary to always consider these warnings real during IMC and nights conditions; and I will continue to do so.  There is no time to examine and diagnose if the warning is real or not.  GPWS/radio alt. faults must be corrected more quickly so as to avoid these scenarios.  It is worth noting that as of my last involvement in this case with this airplane; Maintenance was planning to fly a new radio alt. box to [us] and install it there after only two write-ups.  If this came to pass; then 'great job' to Maintenance for fixing this quickly this time.  This is a safety-critical system and multiple 'can not duplicates' create more hazards.
CRJ-700 Captain reported receiving erroneous GPWS warnings on an approach in IMC; resulting in deviation from assigned altitude. Reporter was critical of company Maintenance response to this ongoing equipment malfunction.