How to Diagnose Spray Foam Hose Heat Issues - Part 1

How to Diagnose Spray Foam Hose Heat Issues - Part 1

How to Diagnose Spray Foam Hose Heat Issues - Part 1

Is something wrong with your spray foam hose heat?

Are you worried you’ll lose hours - maybe days! - of work because you can’t get your hose to heat properly?

Don’t fret! Spray Foam Equipment & Manufacturing has got you covered.

This post acts as a companion to our Hose Heat Troubleshooting video and flow chart. CHECK THEM OUT HERE for step-by-step visual aids!

Now, grab your handy-dandy multimeter - it’s time to roll with the punches, and MacGyver your way out of this issue!

First Things First


That’s how often you want to play around with electricity, willy-nilly like.

We’ll say it again: NEVER.

Electricity can be dangerous - even lethal - if not handled properly.

Don’t let fear stop you, but DO understand what you’re doing BEFORE you do it - and take the necessary safety measures to keep yourself safe.

Bring your trusty friend Common Sense to the party, too. You know - make sure you pay attention to what you’re doing and don’t stand in a puddle of water while you perform these tests, for instance.

Also, make sure you always unwrap ALL of your spray foam hose BEFORE you turn on your hose heat.

If you don’t take your spray foam hose off the hose rack, the overlying hose weight can cause overheating - and even melting - at pressure points along the hose. Not a pretty sight.

There. Disclaimers made. Moving on.

It’s alright - don’t panic! You’ve got the power!

Just use your head.

Okay? Okay.

A Crash Course in Electricity

Current vs. Voltage vs. Resistance

Electrical terminology can be confusing. But you don’t have to be a genius to understand the basics of electrical current, voltage, and resistance.

Just imagine water running through a water pipe.

What does running water in a pipe have to do with electricity?

Well, electrical current, voltage, and resistance are easily compared to our modern plumbing system.

Water pressure (or how much water there is to move through the pipe), flow rate (how fast the water is moving), and the pipe's gauge or size all influence the way that water behaves in the system.  

Voltage - measured in volts (V) - is like water pressure in a water pipe.

Electrical current (I) - measured in amperes (or amps) - is like the flow rate (e.g., gallons/min) of water moving through the pipe.

Resistance (R) - measured in ohms - can be equated to the size of the water pipe itself.

These basic electrical concepts are related to one another. 

More specifically, they are related by a math equation known as Ohm’s Law: 

          Current = Voltage/Resistance or I=V/R.

This equation can be rearranged and expressed as V=I*R and R=V/I as well. 

Main takeaway: changes in current, voltage, and resistance influence each other.  If one changes, so do the others. If you increase voltage, for example (just like if you increase water pressure), electrical current (like water flow) will also increase, provided resistance is kept constant (or the pipe size stays the same).

Alternating and Direct Current

When using a multimeter, it’s important to remember that current is expressed in amperes or amps (A), voltage in volts (V), and resistance in ohms (Ω).

It is also important to note the difference between alternating (AC) and direct current (DC). 

Yes. AC/DC. *Cue the guitar solo*

Direct current is an electrical current that flows consistently and constantly in one direction. Your battery-operated devices like TV remotes and cell phones are powered by direct current.

Alternating current, like its name suggests, alternates in direction via a changing magnetic field. Alternating current allows for electricity to be delivered to our homes from power plants through transformers.  

Transformers - which raise or lower voltage between incoming and outgoing electrical currents - are used in countless applications and require alternating current to function. BOSS spray foam machines use transformers to deliver the correct voltage to your spray hose.

Since the electricity that powers our homes is typically alternating current, anything we plug into our power sockets at home either uses alternating current directly or converts AC to DC to power our devices. 

The batteries in our cell phones, for example, are charged by AC but power our phones using DC.

We know this is a lot of information, but all of these concepts are important to keep yourself safe while working with electricity and directly apply to determining your hose heat issues!

Most of our hose heat diagnostic tests are measured using the AC voltage setting on a multimeter, but we also test for current and resistance periodically.

In the first step, we test the amps of electrical current moving through the power lines of your spray hose without exposing any wires (thanks, clamp multimeter!).  

Later, if we have narrowed down the hose heat problem to a break in the electrical circuit along the length of your spray hose, we will use resistance (in ohms) to test line continuity and locate the break. 

If you don’t feel comfortable performing these electrical tests on your own, contact an electrician for help, or call us here at Spray Foam Equipment & Manufacturing.

Your safety is important to us, and we are here for you.

If your inner MacGyver is rarin’-to-go, however - great!

Let’s get started so you can get back to spraying foam!

Diagnose Spray Foam Hose Heat Issues

Step 1: Test Amperage 

First, you want to make sure your hose heat issue is, in fact, a hose heat issue rather than a temperature sensing issue.

The easiest way to do that requires a clamp-style multimeter. There are several good brands of clamp-style multimeters - Fluke, Milwaukee, and Klein are all brands we recommend. The most important thing about your multimeter is that you know how to use it.

If you don’t have a clamp-style multimeter, you may want to consider investing in one. They can save you time, and time, as you know, is money! If your multimeter does not have a clamp, skip to Step 2. 

With your clamp style multimeter in hand and set to read amps, flip on your machine’s hose heat breaker, and set your hose to call for heat.

Clamp around one of the two red wires running from the machine to your hose. (Either will do.)

When reading amps with your clamp multimeter, you are checking for electrical current in the wires that heat your spray foam hose.  

You want ~35-40 amps of current in the lines.

If your multimeter reads ~35-40 A, great news! 

Your machine is running correctly, and your hose heat problem might be a simple temperature sensing issue.  

To fix this problem, make sure the Temperature Sensing Unit (TSU) wire is secured properly in your hose.

If your multimeter reads below 35 Amps, it’s time to work with machine diagnostics!

Step 2: Test Outgoing Voltage from the Machine

To proceed to this step, TURN OFF the hose heat breaker on your machine.

After turning off the hose heat breaker, you can safely open the compartment at the base of the machine and access the hose heat components.

Use a 5/16 nut or impact driver to remove the cover to the lower compartment. Removing the cover reveals the hose heat transformer, the fuse holder and fuse, and the solid-state relay.  

Take a look at which voltage wires are connected to the fuse box and relay to determine how much voltage your machine should be producing.  

The difference between the voltage wires connected to your solid-state relay and the fuse should be the voltage your machine produces. 

For example, if the 35 V lead is connected to your solid-state relay and the 50 V lead is connected to your fuse, your machine should produce ~15 V to heat your hose.  

Generally, when a BOSS machine is shipped out of our shop with a 50-foot hose, the 0 V lead is connected to the solid-state relay, and the 20 V lead is connected to the fuse. This should deliver 20 volts of power to heat the hose.

If the hose length is increased, there may be a higher voltage wire connected to the fuse when the machine leaves Spray Foam Equipment & Manufacturing. The longer the spray hose, the more voltage is needed to heat the hose.  

Voltage options on BOSS machines are intended to achieve adequate amp draw for BOSS hoses, specifically. DO NOT assume voltage requirements will be the same for alternative brands of hose.

NEVER connect a higher voltage differential than is recommended for our hoses! 

Refer to the following list to determine the correct voltage lead to attach to your machine's fuse for the specific length of your BOSS spray foam hose. (The values assume the 0 V lead is connected to your solid-state relay):

  • 50’ HOSE - 20V LEAD
  • 100’ HOSE - 35V LEAD
  • 150’ HOSE - 50V LEAD
  • 200’ HOSE - 64V LEAD
  • 250’ HOSE - 76V LEAD
  • 300’ HOSE - 90V LEAD


If you intend to move leads around in the lower compartment of your machine, MAKE SURE that the hose heat breaker is OFF!! Go ahead and unplug your machine altogether to be safe.

If the correct leads are connected, or you want to test the voltage coming from your machine, flip the hose heat breaker back on, and set the machine to call for hose heat.

Next, set your multimeter to read AC voltage and connect the probes to the two red wires coming out of the back of the fuse and solid-state relay boxes. This will determine the machine's voltage after it has passed through the fuse and the solid-state relay.  

The voltage between the red wires should be similar to the difference between the two voltages marked on the black wires. 

If the correct voltage is coming from the machine, you know your hose heat issue is located along the hose and not within the machine.

A lower voltage reading than expected could be caused by inadequate power from your generator or power outlet to your machine.

Step 3: Test Voltage from the Transformer

If your BOSS machine is not producing the expected voltage after the fuse and relay (between the red wires), the next step is to test the voltage coming directly from the hose heat transformer.

To test the voltage coming from the transformer, set your multimeter to read AC voltage and touch the probes to the black wires connected to the fuse box and relay. This tests the voltage before it enters the fuse and relay.

If your multimeter reads the expected voltage before the fuse and relay (tested between the black wires), but you have low or no voltage after the fuse and relay (tested between the red wires), you know your machine is receiving adequate power, and the issue lies with either the fuse or the relay. 


You can now isolate the fuse and the relay and determine which needs replacing. 

If you don’t have the correct voltage coming from the transformer, you’ll want to make sure the machine is receiving adequate power.

We will describe how to isolate the fuse and relay and how to test the voltage coming into your machine in next week’s post: How to Diagnose Spray Foam Hose Heat Issues - Part 2.


With some background electrical knowledge, an ounce of common sense, and the proper safety precautions, you can safely perform your own diagnostic tests on your BOSS spray foam machine to determine the cause of your hose heat troubles - right on the job!

This is just another way that Spray Foam Equipment & Manufacturing puts the power back in the spray foam contractor's capable hands.

We will return with Part 2 of How to Diagnose Spray Foam Hose Heat Issues next week.

Don’t forget to watch our complete HOSE HEAT TROUBLESHOOTING VIDEO and peruse the accompanying diagnosis flow chart to help you with your hose heat troubles!

If you have further questions, don’t hesitate to reach out to us.  

Until next time, SPRAY ON!

- The Team at BOSS


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