Control board in Mr. Steam generator installed in San Miguel de Allende (C) Daniel Friedman Steambath Generator Repair
Diagnose trouble with a residential steam generator

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Diagnosis and repair details for electric residential steam bath generator:

This article series describes in detail how, with help from the manufacturer we diagnosed and repaired a new but troubled installation of a residential steam generator in the shower of an existing home.

We explain what went wrong, what trouble it caused, and how steam generator problems with small residential steam generators might be diagnosed and repaired.

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Troubleshooting a New Steam Bath Generator: no steam, error messages

Mr. Steam generator H2O Error Message (C) Daniel FriedmanLet me emphasize at the get-go that the Mr. Steam generator and its controls discussed here is in our opinion an excellent product with superior product support.

The trouble we describe: no steam, water at steam head, error messages at the control, is laid entirely at my own feet as the purchasor and contracting-installer of the equipment.

Bottom line: I took my eyes off of the worker with the hammer drill! The rest is in the details.

Any mechanical system installation that varies from what the manufacturer intended includes a risk that you make a mistake. Having spent nearly 50 years diagnosing problems at buildings and their mechanicals systems I can but emphasize that even if nothing could possibly go wrong, something can and often will.

The property owners tested the new Mr. Steam® generator installation and found it working perfectly after the initial installation. For a few days.

The steam shower, whose enclosing safety glass window and doors were "on order" was sealed for testing using a plastic tarp.

At that time, pending completion of the weather-enclosure the generator, when not in use, was protected by a plastic tarp and was kept successfully dry. Besides, it never rained during that test period.

Steam generator indicator lights for power and water (C) Daniel Friedman

Above: the steam generator control circuit board indicator lights are showing that the unit has power and that it has been properly filled with water.

Then our sheet-metal crew returned to install the weatherproof cover over the steam generator. Thinking that we had plenty of working space, we made a fatal error: we failed to double-check that one of the mounting screws for the steam generator cover might pierce a pipe or an electrical cable.

The site screw drilled pilot holes and screwed the new cover box to the wall. It was a beautiful installation shown at page top and in other photos here.

Area of steam control cable routing near pressure regulator (C) Daniel Friedman

Above, photos showing the location of the steambath generator cover mounting screw that was suspect, and photographs of the control cable conduit during installation showing the area that might be pierced by the cover screw.

Steam generator during installation (C)Daniel Friedman

Above: the steam generator during installation, yellow oval marks area thorough which the control cable conduit passes up the wall to the wall-mounted steam control.

Observation 1: no steam

The owners tested the steam generator that evening. It failed to operate. Steam was not generated and the wall control displayed two error messages.

The wall control power button and temperature control buttons gave no response.

Observation 2: error messages on the wall control

Err2 was followed by H2O - the unit was not sensing that it had sufficient water.

Mr Steam iTempo steam control module, wall mounted - in San Miguel de Allende steam generator system(C) Daniel Friedman Mr. Steam generator H2O Error Message (C) Daniel Friedman

Error codes are explained in Mr. STEAM GENERATOR MS90EC1 INSTALLATION MANUAL [PDF] where you can read that Err2 means it thinks the circuit board override-test button has been pressed for more than 5 minutes, suggesting a problem with the control or its cover.

H2O - a warning shown at the start of this article, means that the system is not detecting sufficient water - the manual lists several possible causes.

Was the problem a misadjusted water pressure regulator, a bad water control valve in the steam generator, or something else?

Steam generator power light - green (C) Daniel Friedman

The green light indicates that the steambath generator has electrical power. Notice that the yellow WTR (water) and red HTR (heater) lights are not lit.

Steam generator water sensor and other controls (C) Daniel Friedman

Above: to the left of the control circuit board you'll see the purple wire connected to a water level sensor probe for the steam generator.

Particularly if the system is being fed hard water, mineral deposits accumulating on the probe's sensor tip can interfere with the ability of the sensor to properly measure water level.

Some water level sensor probe models can be cleaned, others must be replaced if scaling trouble is found.

Behind the sensor probe is the black connector power switch for incoming 240VAC.

We checked the pressure gauge at the pressure regulator and re-adjusted the regulator to be sure we had about 20 psi of incoming water. That made no difference.

Control board in Mr. Steam generator installed in San Miguel de Allende (C) Daniel FriedmanObservation 3: wall control goes dark

Then the wall control went completely dark, refusing to respond to the on-off switch nor its other controls.

Suspecting that a cover mounting screw might have cut the control wires between the wall control and the steam generator's circuit board we tried the on-board over-ride button on the circuit board.

If all else is working this test will give 5-10 minutes of steam generation.

The test cycle using the over-ride button (red arrow in our photo above) resulted in cool water running continuously out of the steam head (photo below).

Did this mean that a water control solenoid in the steam generator was broken?

Probably not. If the solenoid fails you should see either no water or water running continuously regardless of whether the unit has electrical power or not.

Mr. Steam MS90E Steam Generator Errors: Probable Diagnosis:

Water runs out of steam head (C) Daniel FriedmanA call to speak with Mr. Steam's technical support representative led to his conclusion that

Watch out: being careless when drilling and mounting anything along the route of piping or electrical control cables that have been routed within a wall cavity risks causing serious damage to the equipment.

In a wood-framed building wiring is normally protected by steel plates if it passes close to the surface of a wall stud.

But in Mexico a common construction method builds out of solid concrete or out of adobe. After walls and ceilings have been constructed it is common practice to cut grooves in the wall surface for pipes or wires.

After pipes or wires have been installed they are plastered-over. Once the building has been painted, the exact path of these pipes or wires may be impossible to see.

Special thanks to the P.R., Mr. Steam's technical support representative who patiently guided us through the trouble symptoms and recommended the necessary repair parts for this steam generator repair work.

Readers who need help with the selection, installation, or repair of their own Mr. Steam steambath generator should contact the company directly at

Mr. Steam: Sussman Automatic Corporation, 43-20 34th Street, Long Island City NY 11101 USA Tel: 1 800 76 STEAM, or 9410 S. La Cienega Blvd., Inglewood CA 90301 USA, Tel: 1 800 72 STEAM, Tel: 1-800-707-2862 [USA] Website: Email: Sales: Service:


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