Top 5 DIY Mistakes for Service Plumbers to Watch for with CPVC

09 Jun.,2025

 

Top 5 DIY Mistakes for Service Plumbers to Watch for with CPVC

Since , more than 12 billion feet of FlowGuard Gold® CPVC pipe has been installed in the U.S. This product has proven to be extremely reliable, with many systems still in service after 40 or more years.

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However, like any system, a bad installation can cause FlowGuard Gold CPVC to fail. Many of these failures can be attributed to well-intentioned DIYers who simply didn’t have the knowledge, the skill set or the resources of a professional plumber to complete the installation properly.

As a service plumber, it’s important to recognize the root causes of these failures, so that you can repair it properly. Following, we have identified the top five installation questions you should consider when making a repair.

Was the fitting correct?

To ensure a successful installation and years of worry-free performance, FlowGuard Gold pipes must be used with FlowGuard Gold fittings.

However, for many DIYers, all fittings look the same. Its not uncommon for a homeowner to buy white PVC fittings for use with FlowGuard Gold CPVC, but these fittings will not fit on CPVC pipe, even if they are the same nominal diameter. CPVC fittings will be tan in color and will be labeled CPVC. If a PVC fitting is used on a FlowGuard Gold system, it may fail when exposed to the temperatures and pressures seen in a hot and cold-water distribution system. So, during your repair, check to see what type of fitting was initially installed, and make sure that you are replacing it with a FlowGuard Gold fitting.

Was the right cement used?

When a DIYer walks into big box store, they are presented with a lot of different cements choices, including many PVC and ABS options. For the untrained eye, it can be difficult to recognize the difference among the selections and as a result the incorrect option is often chosen. We’ve even heard stories of some people using products like an all-purpose glue, which aren’t suitable for any plumbing application.

To avoid blown joints and costly failures, it’s important to select a cement that is formulated to work specifically with CPVC pipe. For FlowGuard Gold, we recommend FlowGuard Gold one-step solvent cement.

As you are likely aware, solvent cements are color coded, and FlowGuard Gold one-step cement is yellow. If a cement is blue, black or clear, it is not suitable for CPVC applications.

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Was the cement applied properly?

Proper application of the cement is also critical to the job’s success. A heavy, even coat of FlowGuard Gold one-step solvent cement should be applied to the outside of the pipe, with an additional thin coat applied to the inside. If the original installer put too much cement inside the fitting, it can puddle in the fitting causing damage. If they put too little cement on, there could be gaps in the joint which can become leaks.

During your repair, an even bead of cement should be visible around the joint. If it is not, disassemble and remake the joint to ensure system integrity.

Was expansion and contraction accounted for?

CPVC piping expands and contracts in response to changes in temperature. For each 50°F temperature increase, FlowGuard Gold will expand about one inch per 50 feet of straight pipe. This will cause the pipe to move.

Sometimes during an installation, novice installers will restrict the natural lateral movement of the pipe either by overtightening supports, or not leave adequate spacing around supports or joists. While FlowGuard Gold is a robust product that can last for many years under stresses well beyond normal tolerances, it will eventually fail.

Check to see if the lateral movement of the pipe has been restricted and be sure to give the pipe adequate space for expansion and contraction during the repair process.

Were other undue stresses put on the pipe?

Expansion tanks, when improperly installed, can also put stress on the pipe. According to code, these tanks should be mounted. If they’re not, the weight of the tank will pull on the pipe and eventually cause it to break.

During your repair, identify any areas of physical stress that may have caused the failure such as heavy weight or excessive bending stress, and ensure that all pipes are installed and supported properly without excessive stress that may compromise its integrity.

7 Common Speedfit Plumbing and Heating Questions Answered

As a plumbing systems provider of plastic pipes and fittings, RWC get plumbing and heating installation questions put forward to them every day.

In this blog, they look at 7 common plumbing and heating questions asked about RWC’s JG Speedfit products by installers. Even with world-leading plastic plumbing solutions, like the Speedfit range, there can be installation shortcomings during or after install, if not used correctly.

1. Do I need to insulate Speedfit plumbing pipes?

When running heating pipework through walls, it is important to comply with Part L of the Building Regulations. This states that any pipework run through walls in areas that aren’t heated, need to be adequately insulated to prevent heat loss.

This is also the case if service pipework is being run into a domestic dwelling externally, for example cold water, where insulation and seals should be used to properly insulate the entry point.

2. Do I need to use an insert every time I connect Speedfit pipes to a fitting, and why are there two types of insert?

The simple answer is yes, always use an insert when installing Speedfit pipes as it supports the shape of the pipe.

Reliance have two types of insert – the ‘STS’, or Superseal for plastic to plastic, and the ‘TSM’ for plastic to compression.

The ‘STS has an extra O-Ring, which helps to reduce the risk of leaks due to side load.

The ‘TSM’ insert does not have an O-Ring, and therefore allows more pipe into the fitting. This is important when using Speedfit pipe with compression fittings as use of a TSM insert allows the olive to sit further down the pipe. (Only TSM inserts should be used with compression fittings).

3. Can Speedfit pipe be buried in the floor screed?

Building regulations state that pipe laid in floor screed must be removable, with the exception of pipes used in underfloor heating projects.

This exception is important to bear in mind as due to the UK Government’s Build Back Greener strategy, underfloor heating systems are likely to become more common. This is because they are compatible with ground and air source pumps, which are top contenders to replace gas boilers as they are more environmentally friendly.

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In all other projects, pipes laid in the floor screed must be removable, therefore we supply a conduit that can be clipped to the concrete base. The Speedfit pipe can then run through the conduit and be screeded over.

If the pipe needs to be replaced, it can be disconnected at each end and pulled out. The installation of fittings under screed should be avoided, but where it is deemed necessary, they must be installed in boxes with removable lids so that they can be serviced.

4. Can I connect Speedfit pipe directly into compression fittings?

Yes, but only if the pipe and fittings are compatible.

Compression fittings with a short tube stop depth should not be used with Speedfit pipes. Use a ‘TSM’ insert and follow the instructions of the compression fitting manufacturer when connecting to plastic pipework.

5. What is the difference between Speedfit PB (Polybutylene) and Speedfit PEX pipe?

The difference is that the PB pipe is more flexible than the PEX, this is because there is less memory in the coil. Both versions are barrier pipes and can be used for the same types of installation.

6. What temperatures and pressures are your pipe and fittings approved to work at?

JG Speedfit pipe and fittings are approved to work at the following:

• 12 bar at 20°C

•  6 bar at 65°C and,

•  3 bar at 82°C – 105°C max, but the pipes and fittings can withstand 114°C for short periods of time, in case of thermostat malfunctions.

Fittings that are not suitable for central heating have a maximum temperature of 65°C.

7. For plumbing and heating, what pressure should you test pipe and fittings at?

All pipes should be hydraulically tested. You should test your pipes at 2 bar for 10 minutes and then at 10 bar for 10 minutes.

If you have a question on plumbing and heating or the JG Speedfit range of plastic fittings & pipes, please contact the team.

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