My boiler stopped working, what do I check? Here is the honest version: what you can safely check yourself in the next five minutes, what a technician usually finds when it is not that, and exactly what it costs to find out.
By Top Flight Heating, Air & Plumbing, Sussex County, DE. Updated September 27, 2026. Rated 4.9 out of 5 across 522 reviews.
If this means no heat in the house: A home with no heat is treated as urgent and prioritized, often same-day. The emergency button on the booking page gets a callback within 60 seconds.
If one of these fixes it, you owe us nothing and we are glad. If not, the next part is what the visit is for.
No heat. A boiler that will not light has failed to prove its pilot: the module tries four times and locks out, and the pilot, the flame sensor and the gas valve are what it is waiting on. Before the pilot is blamed, the boiler checks its own venting: a spill switch or rollout that has opened, or a vent damper stuck closed, holds the burner off, and it opened for a reason.
Cold radiators. A radiator that stays cold while the rest heat has air trapped in it, or the system pressure is too low to lift water that far. Air keeps coming back because water keeps going out: the manual sends the technician looking for the leak whenever the pressure is low.
Losing water. A boiler that keeps needing water has a leak somewhere in the boiler or the piping, and the manual is blunt about what the constant makeup water does next. Fresh water brings oxygen and minerals: oxygen corrodes the sections from the inside, which is the black water, and the minerals scale them until the deposits are too heavy to remove.
These are the causes in the manufacturers' troubleshooting charts and the trade handbooks our technicians train on, in plain words. The visit proves which one it is with a meter before anything is replaced.
The control module wants clean 120 volt power with the right polarity and a real ground; reversed polarity or a poor ground is a fault light on its own.
A combination fill valve and backflow preventer meters the makeup water and keeps the loop from refilling with fresh oxygen and minerals, which is what the manual says wears the sections.
$59 on weekdays, $159 evenings and weekends. Published and final, pre-tax, and the price is the price whether we find a loose wire or a bad motor.
Book the $59 visit online Or call (302) 329-8003Real arrival windows, including evenings and weekends. Paying is what confirms the slot; the office calls to confirm the window.