Written by
Lena Hartwell Appliance Care EditorPublished October 27, 2026
VERIFIED
Error codeU40 / L40
ApplianceWall Oven
Quick reference
U40 is for a lone or upper oven and L40 for the lower.
The relay board reports a wiggler failure.
Neither cooking nor cleaning can be used.
The manual blames a bad relay board.
The circuit behind it
Command states pass between the logic board and the relay board, and a comparator circuit confirms them. If that circuit fails, the wiggler is not in its proper state, and the control gives it 60 seconds before declaring a fatal error.
Steps in the manual
Go over the communication lines, making sure each contact touches and is seated correctly.
Swap in a new relay board.
This is technician work. Cut power at the breaker and call for service.
Series
The manual covers touch-glass Dacor wall ovens in 27 and 30 inch widths, one or two cavities, without stating the series.
A U40 or L40 needs a technician. Phone (415) 687-5926 and give the model number, the code and what the oven did before it stopped. Details on Dacor wall oven repair are online.
Model compatibility: Dacor reuses codes across series and model years, so U40 / L40 may mean something different on another appliance or generation. Confirm this against your model’s documentation and record your full model number before acting.
Plain language
What this code means
Relay board wiggler failure: the comparator circuit checking logic-to-relay command states failed.
Important safety warning. Do not attempt repairs involving electrical components, gas, water lines, refrigerant or sealed systems. Unplug the appliance if it is safe to reach the outlet, and leave internal diagnostics to a qualified technician.
Seeing this code on your Dacor appliance?
Book a specialist visit for a clear estimate and approval before any repair.
You submit a request with your appliance model and symptom, we confirm an appointment window, and a technician performs an on-site diagnosis. You then receive a clear estimate and decide whether to proceed before any repair begins.
Yes. We provide an upfront estimate after diagnosis. No parts are ordered or installed until you approve the work, so there are no surprise charges.
Replacement parts are selected for the exact model and confirmed with you before ordering or installation.
Service areas are listed on the Locations page. Contact us with your ZIP code to confirm current coverage for your address.
Ready to get your Dacor appliance working again?
Book a repair online or call us — clear estimates and approval before any repair work begins.
