I have a rinnai mk 11 gas heater. Can it be operated without the fan on.

https://www.justanswer.com/plumbing/ag6cf-rinnai-avenger-25-gas-heater-keep-getting.html

Please always include full 'make model (what it is)'.

If it is a Rinnai

Rinnai Gas Heater fault code 11 indicates a no ignition or no gas supply on your gas heater system. ... A gas supply issue may be present if the flame on the gas heater pilot drops in pressure, of if your gas heater does not work then there is no gas supply present.Feb. 10, 2020

What is Rinnai Error Code 11 or 12? - Gas Heater Service ...

There is a video as well

https://www.google.com/search?q=Gas+heater+giving+error+code+11

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[PDF]Operation / Installation Manual - Rinnai

https://www.rinnai.us/.../V_Series_Indoor_25xx_U...

Rinnai America Corp.temperature (shown on the digital remote control) the gas burner will ... Without the connection of a remote controller(s), the Rinnai Water Heater is preset to.

PDF]Tankless Water Heater Service Manual - Rinnai

https://www.rinnai.us/.../100000098_Rev_B.pdf

Rinnai America Corp.Indicates condensing water heater models. ... Rinnai Water Heater Service Manual. 2 ..... Digital manometer or U tube type manometer with 14 inch water column (W.C.) scale, a hose and two .... will flash on the display of the remote controller.

Your Owner's manual should help. No manual, try MFG website, or email their customer service. Or try manualslib.com

Error Code 11 indicates an ignition failure. Check that the gas supply is turned ON. Switch the heater to STANDBY and the ON again. If the burner doesn't light or you continue to have a problem contact your Rinnai dealer.

Hope this helps you and thanks for choosing FixYa. Cheers ...

if possible you should check your gas pressure it should be 3.5 inches of water colum if you are using natural gas

Code 11 is that the unit is trying to light but does not sense a flame after 5 seconds. Usually means you have run out of gas if you are bottled gas. Check your bottles are turned on if you are on LPG, you might need to change over manually. Have you anything else on gas?

11 means no gas / failed to ignite - check the bayonet is fully plugged in properly, they can be hard to plug/unlpug - otherwise you wilol have to take it in for service.

You are right
The gas valve has to come out to remove the fan.
Get a gasfitter to do it.

An error code of 11 equals no ignition. Check gas supply, sparker, flame rod, burner and ground.