Bosch sensixx b20l insert water light

Tell us more: What is the Solid Fuel?-- Coal?-- Wood? Is this a Steam boiler?- or a Hot water boiler?-- It sounds like Hot water, for you mention a pump-- Perhaps it is a Hot Water Circulation pump?
Does the Boiler have a sight glass?-- What is the water level?
Tell us more, so we can help you figure things out.
Mack B.

Copy following link for Bosch troubleshooting resources.
Bosch posts service bulletins.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Install tank-type gas water heater for total $350 and save the whole expensive mess of tankless.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Call Bosch
Gas Products Technical Support: 800-642-3111

That model number is only shown at one website, and that model number is not shown at Bosch.
Open following link for Bosch:
http://www.boschwaterheater.com/BoschHotWatercomHome/GasProducts/tabid/331/Default.aspx
Search of Bosch for that model number shows no result.

Some water heaters do not have a pilot light. Instead they use hot surface igniter rod that glows red hot
The igniter rod ignites the gas after solenoid valve opens and gas flows to combustion chamber.
The igniter rod and heat sensor have to be operational, and have to be positioned correctly for ignition to take place.
If igniter rod is not working, or if heat sensor does not detect flame, then gas solenoid valve shuts down and water heater does not heat water.

Natural Gas: Pilot burner or orfice may need to be cleaned. Pg 11 manual.
http://www.boschhotwater.com/Portals/7/TechManuals/125BL_English.pdf
Most tank and tankless gas water heaters today suggest annual cleaning and maintenance of burner.

Open following links for Bosch troubleshooting resources:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/125BLTechSupport/Troubleshoot/tabid/474/Default.aspx

Before calling service technician, open following link for Bosch troubleshooting resources including parts, contact, possible manual, possible service bulletin covering replacement:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Upvote the help.
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Open following link for Bosch tankless troubleshooting resources, including Bosch contact information, typical manuals, error codes, tech support, parts, fuel-saver calculator, service bulletins, water heater forum, fixya links, disclaimers, and links for finding service technician.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Before calling service technician, read manual for fault finding and possible solutions.
Read manual cover to cover, make sure tankless receives yearly maintenance as outline in manual.
http://waterheatertimer.org/pdf/Bosch_water-wizard.pdf
http://waterheatertimer.org/pdf/Bosch_13P_16P_In.pdf

Following links talk about keeping pilot lit, and describe location somewhat. Bosch water wizard has standing pilot light.
http://www.fixya.com/support/t2961646-water_wizard_10p_pilot_light_keeps_going
http://www.fixya.com/support/t2960079-bosh_water_wizard_10p_pilot_light_keeps
http://www.fixya.com/support/t6182021-bosch_10p_tankless_hot_water

1) The manual does not show diagrams you asked for.

2) Website that sells Bosch parts does not show parts for water wizard, nor does Bosch site for parts: Instruction manual says: replace pilot injector
http://www.boschhotwater.com/HelpfulResources/PurchaseParts/tabid/837/Default.aspx
http://www.houseneeds.com/shop/heatingproducts/waterheating/parts/bosch2400espartsbuy.asp#

3) Searching "pilot injector for Bosch Water wizard" turns up fixya questions which is generally bad news for do-it-yourselfer because it means information sources are through service technician.

4) As a general rule, tankless are not do-it-yourself repairs or installation because they are affected by so many internal and external factors, including air quality, air flow, venting, other gas appliances, gas pressure, gas supply, water pressure, water flow, plumbing problems, water quality, plus internal parts and including any combination of things listed above..
Replacement parts each come will disclaimer.

Add a comment with your experience so others with same-similar problem can benefit.
Send some photos so the internet can see the problem.
http://www.fixya.com/support/r6568559-post_photograph_fixya_questions_answers

Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Before calling service technician, open following link for Bosch tankless troubleshooting resources.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Sounds like a flow sensor may be bad. It may be registering flow when there is none and it sending signal to ignitor and gas solenoid that there is.

Sounds like you have a scaled up heat x get it checked out by a bosch service agent

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.