Alto-Shaam Combi Oven Error Code E01: Low Water
E01 Low Water means the steam generator did not fill to its upper level probe, B1, within 5 minutes after fill valve Y1 opened. Press the Start icon to acknowledge the message and make sure the water supply to the oven is on. If E01 returns at the next fill, a technician needs to check the probe, the valve and the drain parts.
Medium: steam cooking is affected, but the manual says the oven tries to return to normal operation after acknowledgment.
- Code
- E01
- Maker
- Alto-Shaam
- Equipment
- Combi ovens
- Applies to
- Combitherm CT PROformance (CTP) and CT Classic (CTC); Combitherm CT Express / ESi / CCi (older 4-10 and 4.10 units; boiler or generator electric/gas)
What does Alto-Shaam error code E01 mean?
The steam generator is the boiler that makes steam for the cooking cavity. Whenever it needs water, the control opens fill solenoid Y1 and starts a timer, expecting the level to rise until it touches the upper probe, B1. If B1 is still dry after 5 minutes, the control decides the generator is not filling and posts E01 Low Water. Water may never arrive because the supply is shut off or the pressure is low. It may arrive and leak away through a drain pump elbow or past a missing drain cap. Or B1 may be coated with calcium so it cannot sense the water that is there. Pressing Start only acknowledges the message; the oven then tries to return to normal operation, so the same test runs at the next fill and E01 comes back if the cause is still present.
Affected models and control systems
Alto-Shaam Combitherm CT PROformance (CTP) and CT Classic (CTC) combi ovens, electric and gas, in sizes 6-10, 10-10, 7-20, 10-20, 20-10 and 20-20. The manual's table limits this entry to roll-in models, and the CT Express manual shows a matching Low Water Boiler message.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- E01 Low Water on the display
- Steam or combination programs that do not get going
- The message coming back after Start is pressed
Possible causes
Listed in Alto-Shaam's documentation
- Water supply shut off
- Water pressure too low
- Calcium build-up on the B1 probe
- Fill solenoid Y1 malfunction
- Drain pump elbow leaking
- Steam generator drain cap missing
- Drain pump malfunction
- Relay board malfunction
Other likely causes — what usually sits behind error code E01 on this control. A technician confirms which one it is before any part is replaced.
- A clogged inlet screen at the fill valve slowing the fill beyond the 5-minute limit
- A kinked or half-closed supply hose between the wall valve and the oven
Safe checks before calling for service
- Press the Start icon once to acknowledge E01.
- Check that the water shutoff valve behind the oven is fully open and the hose is not kinked or crushed.
- Look under the oven for water on the floor, which would point to a leaking drain elbow. Do not remove any panel.
- If E01 comes back, stop using steam modes and note whether it appears on the first fill of the day or only later.
How a technician diagnoses error code E01
- Read the code and confirm the oven is a roll-in CTP or CTC.
- Measure incoming water pressure at the oven with a gauge.
- Inspect the steam generator drain cap, drain pump elbow and drain pump for leaks.
- Remove probe B1, check for scale and test its wiring for continuity; descale if coated.
- Meter fill solenoid Y1 and confirm it receives voltage when the fill is called.
- Test the relay board outputs; replace it only after the other checks pass.
- The steam generator runs hot, and its panels sit next to live wiring.
- Probe B1 and valve Y1 have to be tested with a meter on the energized circuit.
- A leaking drain elbow or missing cap is found only by working inside the oven base.
How error code E01 differs from similar codes
On CT Express ovens the same number is worded Low Water Boiler, so the text on the screen differs from the CTP and CTC wording.
Technical reference
- Maker documentation
- Alto-Shaam owner support
- Edition
- MN-35949 Rev 08 03/22
- Models / control
- Combitherm CT PROformance (CTP) and CT Classic (CTC); Combitherm CT Express / ESi / CCi (older 4-10 and 4.10 units; boiler or generator electric/gas)
- Section
- Error Codes, pp. 25-31
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Related Alto-Shaam combi oven error codes
Why does E01 come back after I press Start?
Start only clears the message. If the water supply is weak or B1 is scaled, the next fill fails the same 5-minute test.
Can I keep cooking with E01 showing?
The oven tries to return to normal operation, but anything that needs steam depends on the generator filling. Treat steam programs as unreliable until it is repaired.
Is E01 the same as a drain problem?
Not exactly. A leaking drain pump elbow or missing cap is one of the listed causes, because water leaves as fast as it enters.
Need help with Alto-Shaam error code E01?
A technician confirms the cause on site and gives you the price in writing before any work starts.