Vertical central heating pipes dropping from their joints, advice please.

[Simon_66]

Hello, I’m hoping someone out there can help me with a query I have regarding my central heating system. It’s an oil fired system with 16 radiators. I’m not sure when the system was installed but certainly a long time ago, perhaps even when the house was built in the mid 90s.

The radiators are fed by pipes that come directly up through the floor, (in other words there is no pipework that runs along the skirting)

My question is what could cause the pipe to drop from the union that connects to the radiator, as if someone had gripped the pipe from below and just pulled it down. This left a gap of around half an inch. The first time it happened it caused a fair amount of water on the floor. The plumber came
out and repaired the joint. Less than a week later it happened again this time in the immersion heater cupboard where there is a system of pipe work that connects to the radiators on the ground floor. One of these pipes dropped straight down leaving a gap of about half an inch. This has also been rectified but I am concerned that it might well happen again. No work had been carried out on the system prior to the pipes dropping, so they weren't loose.

Any help in identifying the cause would be gratefully appreciated. Many thanks.

 

[ShaunCorbs]

Don’t have a clue normally if it’s been there a while any problems would of shown themselves

 

[Chuck]

Plastic or copper pipes? What type of joint? How are the joints at the top restrained /clipped?

One possible explanation is as follows...

Unrestrained plastic pipe expands in length between 0.07 (PVC) and 0.2 (PE) mm / (m °C) so if the descending pipes are 2.2m long and the CH water changes from 20°C to 60°C each time the boiler cycles on/off there will be between 6 mm and 18 mm of expansion to accommodate. (For copper pipe it is more like 1.8 mm.)

The installer should have clipped the pipework in the ceiling far enough from the tee junctions to allow bending to accommodate this movement. If this is not done, the repeated expansion and contraction of the restrained section of pipe forming the leg of the tee will cause longitudinal tension/compression, which might cause the joint to fail eventually.

 

[Simon_66]

Thanks for your reply. The pipes are a mix of copper and plastic. Both pictures show the pipes after repair. There was a previous failure as shown in the second picture.

 

[Chuck]

Thanks for your reply. The pipes are a mix of copper and plastic. Both pictures show the pipes after repair. There was a previous failure as shown in the second picture.

Ah, okay. My reply (comment #3) assumed the tees were in the ceiling and the descenders went down the wall from there, which the pictures show is not the case.

When you use compression fittings to joint plastic pipe a reinforcing 'insert' needs to be pushed into the cut end to strengthen the wall. I can't see whether this has been done from the photos but I suspect not.