How to Repair a Hydronic Floor Heating System: Common Problems and Solutions

Using plumbing tools to repairPlumbing tools
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Are you having problems with your radiant floor heating system and searching for some useful DIY troubleshooting and repair tips?

Don't worry; we are here to help.

This article will show you how to repair a hydronic floor heating system, the common symptoms and causes, and how to diagnose and fix a problem.

How to repair a hydronic floor heating system: Things to consider

How does a hydronic floor heating work?

Hydronic radiant floor heating systems work by utilizing radiant heat to increase the temperature of the floors and objects while heating the surrounding air.

The greatest advantages of radiant floor heating are even heat distribution, reduced temperature fluctuation, non-drying heat, and enhanced comfort.

The system uses a boiler where water is heated by an electric heat pump or furnace using wood, gas, electricity, and heating oil. There is also a circulation pump to move the heated water through the network of PEX pipes installed under the floor.

Floor heating systems can also use programmable wall thermostats to control the room temperature allowing homeowners to optimize their comfort level.

In addition to the above elements, hydronic systems also use manifolds to divide the main hot water line into individual loops or zones (for each room) and zone valves to control the water flow through each loop.

And you don't have to worry about safety issues because thes systems do not have electrical connections below the flooring.

Hydronic underfloor heating systems are installed using one of the several methods:

  • The staple-up method uses the heat emission plates and PEX pipes installed between the floor joists and under the subfloor. 
  • The staple-down method uses PEX pipes fastened to the subfloor, and lightweight concrete poured on the top.
  • Knobbed mats are rigid plastic sheets with knobs where you snap the PEX piping over which you pour concrete. 
  • In-slab method where pipes are embedded inside the concrete slab.

Common problems with hydronic floor radiant heating

As we could see, hydronic floor systems have many advantages and benefits.

However, they can malfunction, leak, not heating, heat partially, or develop other issues. Some problems are easy to troubleshoot and fix, while others require urgent professional repairs.

The most common problems with hydronic floor heating systems are:

  1. Thermostat issues
  2. Problems with the zone valves
  3. Problems with a circulation pump
  4. Airlock
  5. Leaking
  6. Single zone is not heating up
  7. Multiple zones (or entire system) is not heating up
  8. Circulation pump is running constantly and won't turn off
  9. Pressure issues

Thermostat issues and how to fix

Thermostat for hydronic heatingThermostat for hydronic heating

A defective thermostat is one of the most common sources of problems when your hydronic floor heating system is not working.

These thermostats, which are the low-voltage type, are similar to those used in traditional air-forced heating systems.

They can come with a floor temperature sensor, a room sensor, and separate wire connections for each zone valve.

You could install one or more thermostats depending on the level of control you want. For individual control, you can use one thermostat for each room or a single thermostat with multiple sensors that can still provide customized comfort levels.

Don't worry; this is one of the most manageable problems to fix and is considered a simple DIY project.

Here is what is recommended to do with a faulty thermostat:

  • Carefully inspect the thermostat for physical damages, broken wires, or disrupted power supply. 
  • Check the circuit breaker, as it might have tripped. It often happens that when you reset a breaker, the problems get solved.
  • Use a non-contact voltage tester to check the voltage on the zone valve. If there is no power, your thermostat might be broken, requiring you to get a new one.
  • If the problem is with the malfunctioning thermostat, turn off the breaker before replacing it.
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Zone valve problems and how to repair it

Zone valve for hydronic heatingZone valve for hydronic heating

Hydronic radiant heating systems are usually divided into several "zones," so the system can heat the specific area with different temperatures if needed. Each zone uses its own thermostat and a zone valve which opens up when a particular temperature needs to be reached.

They are powered by electricity (24V) and use a small motor to open or close the element.

If the zone valve is broken, circulation and the room temperature will be disrupted, affecting the work and your comfort. That usually means a zone won't heat up at all.

The zone valve can also jam shut or open, allowing hot water through whether it is needed. When the valve is stuck in an open position, try to tap the valve with a hammer. If it closes, you have a problem with a power head; if it stays open, the valve head is damaged or blocked. You might also need to check whether the manual lever is moving freely.

Replacing a power head is easy and doesn't require you to unsolder the body from the copper pipes.

Valves can also leak either at the connection to the pipe (resoldering is required) or from the element itself (needs replacement).

Here are the instructions on how to replace a zone valve.

  • Turn off the circuit breaker.
  • Disconnect the wires.
  • Turn off the zone valve to disconnect the water supply.
  • Drain all the water from the system.
  • Remove the old zone valve.
  • Solder a new valve into place.
  • Fill the system with water and resume the power.

Problems with a circulation pump

recirculating pumpCirculation pump

If your circulation pump stops working or is occasionally operating, your floor won't warm up as it should.

Normally the pump operates quietly, but if it starts making a strange noise, such as rumbling, humming, or hissing, it may be a sign of a problem.

When the issue happens, the only thing you can do is replace a circulating pump.

Note that before you disconnect a pump, all the water from that loop must be removed and circuit wire connections detached.

Airlock problem

Hydronic systems using PEX pipes are sealed and pressurized.
Sometimes they can develop problems such as the airlock, where air bubbles would reduce or block the water flow inside the system.

So, if the specific zone is not heating up, you might have an air bubble problem.

And to remove the air bubbles from the system, you need to flush the water through that zone.

Water is leaking from the PEX tubing

If the PEX tubing was professionally (properly) installed, there should be no problems such as leaking or hot water flow obstructions.

But, if the tubing gets punctured, kinked, or pinched during the installation, a water leak will cause damage to flooring, ceiling surfaces, and surrounding objects.

The solution to this problem might require you to remove the flooring, break up the mortar, cut and remove the damaged piping, and install a new piece.

Single zone is not heating up

Here are the common reasons and repair tips when only a single zone of your hydronic floor system is not heating up:

  • Stuck actuator pin valve - Use a silicon spray or a pair of long-nose pliers to try to free the pin.
  • Faulty actuator - check the thermostat and electric circuit.
  • Faulty thermostat - check the battery or electrical supply, or reset the thermostat.
  • Wiring issues - talk to your electrician.
  • Flow gauges not open properly on the manifold - adjust the flow rates.
  • Airlock - remove the air bubbles by flushing the zone.

Multiple zones (or entire system) is not heating up

  • Circulation pump malfunction - check the power and electric wiring.
  • The pump relay is defective - talk to your electrician.
  • Isolation valve closed on the manifold - open the valve.
  • The pin valve inside the thermostatic valve head is stuck - use a silicone spray or a pair of long-nose pliers to free the pin.

Circulation pump is running constantly and won't turn off

  • The pump relay is stuck: talk to your electrician to check if there are any electrical problems.
  • Faulty thermostat: reset the thermostat, check the batteries on the wireless model, or replace the element if it is broken.
  • Malfunctioning actuator: talk to your electrician to check if there are any electrical issues on the thermostat or electrical panel.

Pressure issues

Since your hydronic floor heating system is closed, it should keep the water pressure consistent.

If the pressure is low, check the system for leaks on the pipes, manifold, boiler, expansion tank, or other components. With the pressure drop, a system won't work efficiently and will increase your utility bills.

If the pressure rises, you might find water flow restrictions due to a blockage or airlocks.

A failed expansion tank with a malfunctioning diaphragm does not accept water to expand when it heats, resulting in a pressure increase.


Hydronic floor heating systems are very reliable and durable but also break, requiring occasional repairs.

Homeowners would complain that the heating is not working at all, working in some rooms only, partially, leaking, and similar.
While we have covered the most common problems and how to troubleshoot and repair them, note that an improperly installed heating system is often the main culprit. Also, note that radiant heat systems need regular care and cleaning to keep them running efficiently.

And that is why we recommend you call a professional because they can diagnose the problem quickly and efficiently and fix it in no time.

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