SHI System Maintenance & Troubleshooting 3 — Questions and Answers
Question 1: A technician finds that the solar loop pressure is 15 PSI above the system design pressure. Which component is most likely malfunctioning?
- Expansion tank is waterlogged or undersized (Correct answer)
- Pressure relief valve is set too low
- Differential controller is overdriving the pump
- Check valve is installed backwards
Correct answer: Expansion tank is waterlogged or undersized
A waterlogged or undersized expansion tank cannot absorb thermal expansion, causing system pressure to rise excessively.
Question 2: When flushing and recharging a propylene glycol solar loop, why must you avoid introducing air bubbles?
- Air reduces glycol freeze protection effectiveness
- Air pockets cause cavitation, heat transfer loss, and pump damage (Correct answer)
- Air increases glycol pH, accelerating corrosion
- Air makes the differential controller read incorrectly
Correct answer: Air pockets cause cavitation, heat transfer loss, and pump damage
Air trapped in the loop causes cavitation in the pump, reduces heat transfer at the collector and heat exchanger, and can cause noise and vibration.
Question 3: A homeowner reports a rotten-egg odor from their solar water heating system. What is the most likely cause and corrective action?
- Degraded glycol producing sulfur compounds; replace glycol
- Anaerobic bacteria in the storage tank; raise tank temperature or disinfect (Correct answer)
- Copper corrosion from acidic water; install neutralizer
- Collector overheating releasing absorbed gases; add pressure relief valve
Correct answer: Anaerobic bacteria in the storage tank; raise tank temperature or disinfect
Sulfur-reducing bacteria thrive in warm but not hot storage tanks, producing hydrogen sulfide; disinfecting the tank and maintaining higher temperatures eliminates them.
Question 4: After replacing a failed circulator pump in a solar loop, the new pump runs but flow is much lower than expected. What should you check first?
- Controller wiring polarity
- Pump rotation direction and air purging (Correct answer)
- Collector tilt angle
- Expansion tank pre-charge pressure
Correct answer: Pump rotation direction and air purging
A pump installed with reversed rotation or with air trapped in the loop will move significantly less fluid than its rated flow.
Question 5: Which glycol property MOST directly indicates it needs replacement, regardless of freeze point readings?
- Color change from pink to clear
- pH below 6 or above 9 (Correct answer)
- Concentration below 40% by volume
- Viscosity increase above 10% from baseline
Correct answer: pH below 6 or above 9
pH outside the 6–9 range indicates inhibitor depletion and acid formation, which causes corrosion of metals in the loop regardless of freeze protection level.
Question 6: A flat-plate solar collector is producing only 60% of its rated output on a clear day at correct flow rate. The glazing is clean. What diagnostic step should you perform next?
- Check differential controller calibration
- Measure inlet and outlet fluid temperatures and calculate heat gain (Correct answer)
- Inspect roof structure for shading obstructions
- Replace the absorber plate
Correct answer: Measure inlet and outlet fluid temperatures and calculate heat gain
Measuring actual inlet and outlet temperatures allows you to calculate real heat output and compare it to the rated value, isolating whether the problem is in the collector or elsewhere.
Question 7: What is the correct procedure for testing a pressure relief valve (PRV) on a solar thermal system during a maintenance visit?
- Open fully and leave open for 30 seconds to clear debris
- Lift the test lever briefly to verify the valve opens and reseats cleanly (Correct answer)
- Replace the PRV annually regardless of condition
- Pressurize the system to PRV set point and confirm it opens
Correct answer: Lift the test lever briefly to verify the valve opens and reseats cleanly
Briefly lifting the test lever confirms the valve opens freely and reseats without leaking, which is the standard operational test without overpressurizing the system.
SHI System Maintenance & Troubleshooting 3
A technician finds that the solar loop pressure is 15 PSI above the system design pressure.
Which component is most likely malfunctioning?