Solar Hot Water System Troubleshooting Table
For Pressurized (PS) and Drainback Systems (DS)
by Bob Ramlow & John Hippensteel





Insufficient heat


Collector loop shows loss of pressure

Collector loop airbound

*Check for and repair leaks

*Check Pressure Relief Valve

*Check air vents if present

*Refill and re-purge system

(PS + DS)


Leak in collector

*Repair or replace absorber plate or vacuum tube


No fluid flow in solar loop

High-head pump airbound

Pump improperly located - relocate



High-head Pump failure

Replace pump



High-head Pump undersized

Upgrade pump



Collector loop Piping sagging

Check for sagging pipes, repair and add pipe hangers (one every 4' min.)



Pump OK but pump does not run

See Systems not running at correct times


Collector loop shows no loss of pressure

Collectors not receiving energy or undersized

*Check collectors

  • Orientation
  • Tilt
  • Shading
  • Size of load
  • Dirt on collectors



Collector loop airbound

Repurge system



Circulator impeller Jammed

*Strike sharply when power is applied to free rotor

*Replace pump cartridge or pump

(PS + DS)


Valves or pump isolation valves shut off

Open valves



Bent or crushed pipes

Repair/replace pipe



Individual tubes in evacuated collector failure

Inspect and replace as needed



Obstruction on collector loop

*In the collector array, unequal collector outlet temperature will show obstructed collector

*Check heat exchanger

*flush & refill



Potable water lines airbound

*Check air vents in potable water lines for proper location and operation

*Check for air in potable water side of heat exchanger



Heat exchanger, Pump(s) or piping too small

Check sizing charts and correct



Faulty or incorrectly installed check valve

*Confirm flow is in correct direction

*Check for correct valve operation

*Check for blockages



Tempering valve set too low or not operating properly

Reset or replace


Large pressure fluctuations in collector loop

Air in loop

*Check for leaks and repair

*Check pressure relief valve and replace if necessary

*Check air vents (if any) and replace or isolate if necessary

*Purge air from system



Expansion tank

*Check expansion tank for fluid in air chamber and replace if necessary

*Make sure to set expansion tank pressure to 25# before installing

*Expansion tank too small. Calculate proper size and replace if needed


Storage tank loosing heat, especially at night

Tank poorly insulated

Insulate tank to R-10 or more if the tank is in a poorly insulated area



Reverse thermosiphoning

Inspect check valve and replace if needed


Piping loosing heat

Improper or insufficient insulation

Repair or replace


Storage tank gets hot quickly but also runs out of hot water quickly

Storage tank too small

Increase storage tank size or add a second tank


Solar tank warm but back-up water heater not warm

Faulty back-up water heater

Repair or replace


System does not run consistently

Controller, sensor or wiring problems

See Systems not running at correct times


Gradual performance decrease

Collector shaded

Clear obstruction



Collector glazing dirty

Clean collectors



Excess condensation inside collectors

*Check collector vents or weep holes and clean if needed

*Check for a slow leak inside collector and repair/replace as needed



Pipe insulation degrading

Replace as needed



Heat exchanger clogged

Check for proper fluid flow through heat exchanger (both sides) and clean or replace as needed

Systems not running at correct times (PS+DS)

Pump(s) running all the time

Controller switch in "ON" position

Move switch to "Auto" position



Collector sensor or leads shorted or storage leads broken (find with ohmmeter)

Correct malfunction. Replace sensor if needed


Pump(s) never running

No power to controller (AC powered)

Restore power



Controller switch in "off" position

Move switch to "Auto" position



Storage sensor leads shorted or collector sensor leads broken (find with ohmmeter)

Correct situation. Replace sensor if needed


Pump(s) running at intermittent times

Corroded or loose sensor wire connections

Clean wire connections of corrosion and re-connect with watertight connectors or solder connections. Never use wire nuts on sensor wiring.



Sensor leads run near 110 VAC wiring

Move sensor wire at least 6" away from 110 VAC wiring or use coaxial cable



Sensors incorrectly placed, poorly secured or improperly insulated

Move sensors to correct location and properly insulate



Sensors improperly wired

Rewire following instructions supplied with the controller


Any of the above

Faulty controller

Check controller and replace as needed


PV powered systems

Loose wiring connections




PV panel undersized

*Check wire size chart for proper wire size and replace wire as needed

*Replace PV panel with proper size

There are a host of good reference materials available, some of which are listed here.
Solar Domestic Hot Water Systems - Repair & Maintenance Manual, FSEC-GP-34-88
John Harrison, Bruce Holbaugh, & Tim Merrigan
Published by the Florida Solar Energy Center
Solar Hot Water Systems - Lessons Learned - 1977 to Today
Tom Lane
Solar Water Heating:  A Comprehensive Guide to Solar Water and Space Heating Systems
Bob Ramlow
And don't forget the manufacturers specification and installation manuals.

Thanks to Kari Heinrich for providing this table, which was produced for the Focus on Energy solar hot water
conference in the Wisconsin Dells, Dec. 2007.