SYMPTOMS:
- Boiler makes banging or gurgling noises
- Water dripping from the flue pipe
- Rust or corrosion showing up early
- Boiler shuts down unexpectedly or short cycles
If you've seen any of these, it's a sign something’s not right — and it usually shows up when you're running a low-temperature system with a non-condensing boiler.
THE PROBLEM:
Non-condensing boilers aren’t made to handle cold return water. When the return temperature drops below about 130°F, it causes condensation inside the heat exchanger. That moisture leads to rust, corrosion, and can kill the boiler long before its time. It's a common issue in systems like radiant or low-temp baseboard where the water coming back is cooler than the boiler can handle.
THE FIX:
Install a bypass loop between the boiler’s supply and return lines — and add two valves and a return temp gauge. This lets you control how much hot water gets recirculated back to the boiler, keeping return temps above the danger zone.
Here’s How to Set It Up:
1. Install a bypass pipe from supply to return.
2. Add Valve A on the bypass pipe itself.
3. Add Valve B on the supply pipe, after the bypass tee.
4. Install a temperature gauge on the return line going into the boiler.
How to Dial It In:
- Start with both valves fully open.
- Let the boiler run under a real load — not just short cycling.
- Watch the return temperature on the gauge.
Then adjust:
- If the return temp is below 130°F, slowly close Valve B (the supply valve) to force more hot water back through the bypass.
- If the return temp is already above 130°F, slowly close Valve A (the bypass valve) to reduce the amount of water short-circuiting back to the boiler and send more flow out to the system.
That’s it. Just a couple valves and a little tuning — and you’ll protect your non condensing boiler from condensing and extend its life.