HRV / ERV (air exchanger) isn't running or isn't ventilating

Q: HRV / ERV (air exchanger) isn't running or isn't ventilating

In Canada, most newer tight homes rely on an HRV or ERV (air exchanger) to swap stale indoor air for fresh outdoor air, so when it stops the first things to rule out are simple: check that the wall control or dehumidistat is actually set to run and not sitting in standby, then wash the filters and rinse the core, which clog on a schedule. In a deep cold snap a brief pause is often a normal defrost cycle, and a frozen or clogged condensate drain or an iced-over exterior hood are winter-specific culprits. A dead motor, a failed control board, or a tripped breaker for the unit is a licensed-HVAC repair. If you ever smell something hot, electrical, or burning from the unit, cut its power and call a technician.

A quiet air exchanger is easy to miss and rarely an emergency — most of the time the control has been left off or the filters are overdue for a wash, and both are a ten-minute fix.

tuneWhat are you noticing?

Select anything that matches and the checklist below reorders to fit. Not sure? Skip it.

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Start here

In Canada, start at the control, because an air exchanger only runs when something asks it to. Find the wall control or dehumidistat and make sure it's switched on and set to a running mode — not standby, and, on a dehumidistat, not a humidity setpoint so low the house never triggers it. Bump it to a continuous or high setting and listen for the unit to spin up. Free, and the single most common reason a healthy HRV sits quiet.

Ranked from real-world failure data. The order updates as you select what you’re noticing above.

Likely causes, in the order to check them

Showing the typical order

Beginner-friendly Doable, with care Safety-critical Call a pro

handymanHow to fix it

Open the front cover, pull the two filters and the recovery core, vacuum and wash the filters, rinse the core under lukewarm water, let everything dry, and slide it all back in the same orientation.

Switch the unit off at the control and open the front cover (usually clips or thumb-latches — no tools).
Slide out the two filters. Vacuum the loose dust, then wash them in lukewarm soapy water and set them aside to dry fully.
Pull the block-shaped recovery core straight out. If it's a washable type, rinse it under lukewarm water in the direction of the passages — never use hot water or a pressure washer, which can warp it. Some ERV cores are NOT washable; check the label and replace instead if so.
Once everything is dry, reinstall the core the same way it came out (there's usually an arrow or label for orientation), slide the filters back, close the cover, and set the control back to its normal running mode.

schedule25 min savings$0–40

HRV/ERV replacement filter setMatch your unit's make/model — filter sizes are model-specific; some ERV cores are replace-only, not washable

gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: homeowner may do this
Cleaning HRV/ERV filters and the recovery core is routine homeowner maintenance in every province.

visibilityHow to check

warning Warm water only, and don't force the drainUse warm water, never boiling — a sudden temperature shock can crack a plastic drain or trap. Don't jam wire or tools down the line to clear ice; you can split it. If the drain keeps freezing, that usually means the routing or heat trace needs a look, and that's a job for a licensed HVAC technician rather than a repeat DIY thaw.

Note the timing. If ventilation stops only for a few minutes during a cold snap and restarts on its own, that's very likely a normal defrost cycle — leave it be and watch whether it recovers.
If it's stopped for good, find the condensate drain line and trap underneath or beside the unit and look for ice, a kink, or standing water — signs the drain is frozen or clogged.
Flush the drain and trap gently with warm (not boiling) water and clear any visible debris. If water runs through freely and the unit restarts, you're done; if it re-freezes or the drain won't clear, the drain routing or defrost controls need a technician.

buildNo tools schedule15 min

visibilityHow to check

warning Mind the ladder and the iceExterior hoods are sometimes mounted high or over hard, icy ground. Don't overreach from a ladder in winter conditions, and don't chip aggressively at ice around the hood — clear it gently. If a hood is out of safe reach or keeps icing over, it's reasonable to hand this to a technician instead of taking a fall.

Go outside and find the two vent hoods for the air exchanger — usually a pair on the same exterior wall, one drawing fresh air in and one pushing stale air out.
Look for a glaze of ice, packed snow, matted leaves or lint, or a bug/bird screen clogged with debris. Either hood blocked will choke the unit.
Clear the blockage gently by hand or with a soft brush. If a hood re-ices within a day or two, the defrost system may be undersized or faulty and should be checked by a technician.

buildNo tools schedule10 min

verifiedWhy this one goes to a pro

Beyond resetting a tripped breaker once, diagnosing a failed blower motor or control board means working on the unit's live line-voltage wiring. In Canada that's licensed work, and a board or motor that fails can also point to an underlying fault a technician needs to find. Cut power at the breaker and book an HVAC tech — it's a fast diagnosis for someone with the meter and the training.

gavel Check your province first AB: licensed professionals only · BC: licensed professionals only · ON: licensed professionals only · PE: licensed professionals only · QC: licensed professionals only
Line-voltage motor/board repair is licensed electrical/HVAC work in every province; confirm local rules. A homeowner may reset a tripped breaker only.

Your notes travel with the request — what you saw, what you ruled out, when it started — so the pro arrives with a head start instead of a mystery.

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Why the list is in this order

We don’t sort by likelihood alone. We sort the way a good, honest tradesperson thinks: rule out the free, safe, common causes first. That’s why the cheap checks outrank the expensive repairs — and why anything dangerous gets a hard stop instead of a pep talk. The order exists to save you money, not to sell you anything.