Blinking light on ae125 tankless water heater

SOURCE: A2 error on Bosch tankless water heater

1. Check continuity of the flue gas limiter (see Fig. 63, page 46 of manual). Go to steps two and three to determine air box temperature sensor fault and replace it.
2. Check for flue gas leakage around the top and bottom seals of heat exchanger as well as the viewing window.
3. Check that venting is within specifications (see Section 3.3 of manual). Long vent lengths, venting with more than three elbows, blocked vent or combination venting may cause this failure.
4. Check that flue gas limiter connector and spade connections are secure.
5. Unplug heater and check the two main plug connections inside the control board.

SOURCE: Tankless water heater pilot light will not stay on

It is most likely the water valve stuck open, telling the controls to heat water, that it thinks is flowing through it, but without actual flow it overheats. Depending on how comfortable you are with taking it apart yourself, you could open the valve to see if it just needs cleaned out, or if you have a ruptured diaphragm or some other cause.

Ned C Cook

• 3433 Answers
• Posted on May 06, 2009

SOURCE: no hot water, pilot light lights but no burner ignition

Thermo coupler may be defective. it controls the main gas valve by closing main if pilot is out. make sure thermo coupler bulb is positioned over and near tip of pilot flame, but not in the flame. Thermo couplers are inexpensive and easy to change out.

Steven Foerst

• 52 Answers
• Posted on Apr 11, 2010

SOURCE: i have a 250SX aquastar bosch tankless hot water

The 250 MUST have the condensate line connected. EC comes from gas supply problems and CO2 levels not being adjusted. LP units require 3/4" smooth gas pipe or 1" corrugated pipe minimum size. The LP regulator needs to be turned up to about 13 inches of water column and with all the gas appliances on, measure no less than 11 inches of water column. The CO2 levels must be measured by a qualified gas technician with a calibrated (with in 6 months) CO2 analyzer.

SOURCE: I have a Bosch AquaStar AQ-125-BNG tankless water

there is a small dia copper pipe which has a thermal coupling on it the end of it sits in the flame of the pilot light,
if it fails which it does after about 25-15 months,it shuts down the gas burner