Troubleshooting Radiant Heat Systems

June 1, 2003
by Ron Beck Troubleshooting radiant heat can be quite simple or very extensive depending on the system. First, determine what type of radiant system youre

by Ron Beck

Troubleshooting radiant heat can be quite simple or very extensive depending on the system. First, determine what type of radiant system you’re working with: stapled-up, in-slab, various types of gypcrete or lightweight concrete. You must also know the types of floor coverings and how the water temperature and room temperatures are controlled.

While determining this, your greatest challenge will be locating all the supply and return manifolds. Manifolds are usually scattered throughout a building because it’s better to keep them closer to the areas they control rather then in the boiler room.

Now it’s time to determine how much air space the system was designed for. If the owner is complaining of not having enough heat in a given area, the system may not have been designed to provide as warm a temperature as he or she wanted. This normally happens only on a design temperature day.

An important question to ask owners is whether they’ve changed the floor covering. It may be a new home, and the floor covering could have been changed on the plans without the heating contractor being aware of it. If the floor covering was changed, determine by how much using information from Chart 2. You might be able to adjust the water temperature up enough to compensate for the higher R-values. When adjusting the water temperature keep in mind that the floor surface temperature should never exceed 85F, or the manufacturer’s suggested maximum temperature.

Now, check to see if the circulator is working properly. Radiant floor systems are usually designed for a temperature drop through the system of 15F to 30F. You need a way to measure the supply and return temperatures to see if the circulator is moving enough water. Start with a warm system. Don’t perform a temperature check when you first turn the system on.

If the temperature drop is too large, the circulator may be undersized, or the zone may not be warmed up yet. The flow restrictors might be closed down too far and the water isn’t moving fast enough through the tubing.

If the temperature drop is too small, the circulator may be oversized. The water and floor may be very close to the same temperature and not transferring much heat. If the room is too cool, check your floor temperature. If it’s less then 85F, you can increase the water temperature.

Another potential problem involves the mixing valve. This valve has three piping ports. The hot port, which is the hot supply water from the boiler; cold port, which is the return pipe from the radiant loop; and the mix port, which is the warm supply pipe to the radiant zone. The valves are adjusted to a design temperature and will automatically adjust hot and cold water to maintain that given temperature in the radiant heat zone.

If a complaint says the floor temperature is too hot or too cold, check the mix temperature and compare it to the setting of the valve. Change the setting and see if the water temperature goes up and down.

If the manufacturer’s installation manual is still on the job site, verify that the mixing valve is set on a number that coincides with the water temperature leaving the mixing valve. If it’s not accurate, most of these valves have a replaceable mechanism. You don’t have to replace the whole valve.

One last note: make sure the circulator is pumping away from the mix port.

To make troubleshooting easier next time, leave the heat loss print out and piping diagram on the jobsite. The heat loss provides information on the gpm flow required and loop temperature — a good starting point for adjusting the flow restrictors or circuit setters. Maybe one wasn’t set properly, or none were adjusted at the time of installation.

Check Outdoor Reset Controls

If you haven’t resolved the problem at this point, it’s time to examine the outdoor reset controls. Many radiant systems use outdoor reset controls to increase and reduce water temperature in the radiant zone as the outdoor ambient temperature changes. This is set with the heating curves, and both supply water and outdoor air sensors.

Heating curves may seem confusing at first, but are actually very simple. The heating curve could be a 0.5, 0.7, 1.0, or whatever the manufacturer uses. The 0.5 heating curve means for every 1F the outdoor temperature changes, the water temperature changes 0.5 or 12F. A heating curve of 1 means for every degree the outdoor ambient changes the water temperature changes 1F. Another way of looking at heating curves is 1 - 0.5 or 1 ¯ 1.

The outdoor air sensor should be mounted in a shady location. Most of these sensors are called 10K sensors. This means they’re 10,000 ohm sensors. If the water temperature is off, check with a Volt-Ohm meter for proper resistance for the given outdoor and supply water temperature. The readings won’t be completely accurate, but should be close. If not, replace the sensors.

It’s also a good idea to check the control. Pick an outdoor temperature and buy a resistor to match the ohms reading you should have at that temperature, based on the manufacturer’s instructions. Disconnect the outdoor sensor and connect the resistor to the outdoor sensor terminals. The water temperature should readjust to the new artificial outdoor temperature. This may take a few minutes.

Another popular way of controlling radiant loops is to use injection pumping. Here, you have a boiler loop, a loop other radiant loops branch from, and a small injection loop. This works similar to an automatic mixing valve except it’s operated electrically. There’s a sensor on the supply pipe and on the injection pipe.

There’s also an outdoor sensor. The control senses outdoor temperature and compares it to supply water temperature. It then mixes the right amount of boiler supply water to bring the radiant zone water temperature to the required setting. You can use resistors of the proper range to troubleshoot an injection pumping control system.

Finally, if you suspect a circulator problem, keep in mind that it’s harder to troubleshoot wet rotor circulators then the older coupling types. Look at the bearing assembly. Is the coupling spinning? That’s a good indicator the circulator motor is working.

With the wet rotor, check amperage. If the circulator is energized but not running, you’ll see an amp increase of about 40% or greater if the circulator is trying to start. If it’s completely burned out, you’ll get next to nothing. Remember, the amperage will change as incoming voltage changes.

There are so many variables on radiant systems, from how the tubing is installed to what controls are used, that this troubleshooting guide just skims the surface. If you have more questions, the Burnham Hydronics technical department can be reached at 717/397-4701 or e-mailed at [email protected].