. Turn the gas OFF to the water heater and press the piezo igniter. Once pressed, the electrode should release the spark. Check if the wire connection is tightened correctly. Make sure the electrode is not broken, and replace it if it is. Soot and/or carbon deposits on the pilot light. Honeywell WV8840B1042 status light will not come on when I try to relite nevertheless I have over 500 mill volts coming from the thermocouple. ... (with a nine volt battery) do you think it is worth a try again does the entire system reset. ... This unit acts like it needs a new thermocouple and what's sold normally for thermocouple replacement. The battery is a 3.6v Ni-MH cell as made by Varta. I hear later variants of the ST699 may have the battery fully soldered to the board so before rushing out to buy a replacement, take a close look to ensure you are getting the right cell. Series 5000 Honeywell Thermostat Battery Replacement- Tested Models TH5110D, TH5220D & TH5320U. Series 5000 comes with Auto changeover feature which enables to switch between heating and cooling both by accessing the temperature of the room. The thermostat comes with a sliding battery compartment and you do not have to open the cover from the.