The inlet filter on Stiebel Eltron Tempra Plus and DHC tankless protects the heating chamber from debris that could damage the heat exchanger or jam the flow sensor. It\'s also the most-neglected maintenance item — and the cause of most "flow sensor failure" calls.
Why it clogs
- New construction debris — flux, solder bits, pipe shavings carried by water during first weeks
- Old galvanized plumbing — rust flakes from older homes
- Hard water — calcium carbonate scale builds on the screen
- Sediment from municipal main breaks or system maintenance — episodic events deposit batches of debris
Symptoms of clogged filter
- E1 error (no flow) when flow is actually present at the meter
- Reduced flow rate at hot taps over time
- Output temperature drops because Flow Control sees inadequate flow
- Audible flow restriction at the unit (whistling or hiss)
Cleaning procedure (Tempra Plus)
- Close inlet shutoff upstream of the Tempra
- Open a hot tap downstream to relieve pressure
- Locate the inlet filter housing at the cold water connection (typically threaded service fitting)
- Catch any residual water with a towel or small bucket
- Unscrew the housing with a wrench
- Remove the strainer screen — typically a small cylindrical mesh
- Rinse under running water — clear all visible debris
- Soak in vinegar for 15-30 minutes if scale is heavy
- Inspect for damage — replace if mesh is torn or corroded
- Reinstall strainer and housing
- Reopen inlet shutoff slowly — verify no leaks
- Close hot tap when steady flow returns
Cleaning frequency
- First 6 months after install: check monthly (construction debris)
- After year 1: annual cleaning minimum
- Hard water installs: every 6 months
- After municipal water main work: immediately
Replacement
- Stiebel inlet filter screen: $10-20 OEM
- Generic 80-mesh strainers may substitute if Stiebel part unavailable
- Filter housing rarely needs replacement — clean and reinstall
Upgrade: whole-house pre-filter
For Tempra Plus installs in homes with known sediment issues, install a whole-house spin-down sediment filter ($60-120) upstream of the water heater. This protects ALL appliances (dishwasher, washing machine, ice maker) and dramatically reduces Tempra filter cleaning frequency. The Rusco brand is widely used for this application.
Bottom line
The inlet filter is Stiebel Eltron\'s most-important maintenance task. 10 minutes annually prevents 80% of "flow sensor" issues. If you only do one Stiebel maintenance task per year, do this one.