UFH Pressure Test Length / Pressure Dropping

[jamesmonk83]

Hi All,

My wife and I our renovating our first house together and have become a little stuck installing our wet underfloor heating system. Before we end up phoning around local plumbers I thought I'd post on here to see if anyone has any bright ideas.

We've laid the pipes (2 zones), attached the manifold to the wall with the ball and drain/fill valves and run water around the system from the mains (one circuit at a time) as per the manufacturers instructions. We've carefully gone around checking the pipes and there are no signs of any leaks so we started pressure testing the system. At first there were obvious leaks around all the valves so we re-fitted them and tightened them up which has stopped that however the pressure isn't holding for very long. According to the manufacturers instructions the system needs to be at 6 bar for 2 hours. Our system does appear to hold the pressure for this long however whenever we've left it overnight it always drops by around 1.5 bar. We're not sure whether this is normal or something to worry about? We've doubled checked all the connections on the manifold and there are definitely no signs of any water/leaks and the pipes aren't leaking so we're a bit mystified as to the pressure would drop like this.

Any help/advice would be greatly appreciated.

James

 

[oz-plumber]

Could either be a drop in the ambient temperature overnight or the pipework expanding due to the pressure in the pipes.
As the pipe expands, it increases the volume of the pipe and hence the drop in pressure.
I'm sure if you read the instructions from the pipe supplier, they will give you instructions how to counteract this pressure loss and the procedure of how to do it.

But if you can't see any visible leaks in the pipe you are probably OK

 

[Chuck]

According to the manufacturers instructions the system needs to be at 6 bar for 2 hours. Our system does appear to hold the pressure for this long however whenever we've left it overnight it always drops by around 1.5 bar. We're not sure whether this is normal or something to worry about?

Did the manufacturers tell you to leave pressurised at 6 bar overnight? If not, don't. The reason iis that if you leave plastic pipe pressurised for extended periods it deforms (stretches) permanently, which probably explains your pressure drop.

You asked for advice:

First rule for these systems is follow the manufacturer's instructions to the letter. Also, take photographs of work in progress and record the results of any tests.

Personally, I don't think it is wise for amateurs to install UFH. A lot of details need to be got right with design, installation and commissioning and the cost of fixing problems is often high. Worth paying a professional who does them week-in week-out for their experience. Save money elsewhere.

 

[jamesmonk83]

Thanks for the replies, to be honest the written instructions from the manufacturer aren't very detailed or helpful. There are a number of YouTube videos detailing the process (from the manufacturers) which we've been following throughout the process but nothing much on trouble shooting.

Did the manufacturers tell you to leave pressurised at 6 bar overnight? If not, don't. The reason iis that if you leave plastic pipe pressurised for extended periods it deforms (stretches) permanently, which probably explains your pressure drop.

The reason for keeping it at 6 bar is because this is the recommended pressure that the pipes need to be kept at whilst the screed is being laid.

 

[townfanjon]

What are you using to test the ufh ?

 

[jamesmonk83]

What are you using to test the ufh ?

It's a Rothenberger RP30 pump.

 

[oz-plumber]

DIY install + Youtube = no manufacturer warranty, no insurance cover, no guarantees and sleepless nights.

 

[Dave Marques]

6 Bar might be the max pressure for the initial test. Normally the test drops to say a min of 2 bar for 1 hour. The system should be under pressure while the screed is laid but that may not mean the 6 bar max, best check with the supplier tech desk.

 

[jamesmonk83]

6 Bar might be the max pressure for the initial test. Normally the test drops to say a min of 2 bar for 1 hour. The system should be under pressure while the screed is laid but that may not mean the 6 bar max, best check with the supplier tech desk.

Sorry I probably should have mentioned that the manufacturer says the pressure shouldn't exceed 8 bar once the screed is laid.

 

[ShaunCorbs]

Did you flush the pipework to make sure there’s no air left in the system as this can move it a bit ?

 

[oz-plumber]

What pipe did you use and who is the manufacturer?
If you have serious concerns about the pipe and testing criteria, it may be worth contacting them or the wholesaler you bought the product from.

We can only give advice and reassurances - nothing else.
UFH system leaks are awfully expensive to fix and repair and if the system is not done right, then it will be a complete waste.

 

[centralheatking]

The difference in pressure on a conventional 3 bed semi on a combi system between 1.5 bar and 0.5 is in reality only 2 litre at most over a relatively narrow temp range. Water is not really compressable.
You need to consider the volume in your installed system. Its been very warm recently with quite dramatic highs maybe you are ok.
I have many years experience in conventional ch etc. but if I was to contemplate underfloor ...I would only install on a new build due to thermal performance and insulation criteria AND I would get one of the expert on here to come and do the lot. centralheatking

 

[jamesmonk83]

Did you flush the pipework to make sure there’s no air left in the system as this can move it a bit ?

Yes we did this before testing each time.

What pipe did you use and who is the manufacturer?
If you have serious concerns about the pipe and testing criteria, it may be worth contacting them or the wholesaler you bought the product from.

We can only give advice and reassurances - nothing else.
UFH system leaks are awfully expensive to fix and repair and if the system is not done right, then it will be a complete waste.

Understood, I guess we were just wondering whether any other reason could cause a drop in pressure other than a leak.

The pipe is Pex-Al-HDPE pipe from ProWarm.

Its been very warm recently with quite dramatic highs maybe you are ok.

Yes we did wonder whether this would make the pressure rise and fall (which it has done over the past few days) however we first tested the system over a week ago before we had this warm spell and the temperature was pretty regular and it was still dropping. It always seems to fall at the same consistent rate so we were wondering whether this is the norm when a manifold isn't connected to a pump/boiler etc.

 

[SimonG]

Is the screed down?
Are you sure you got all the air out?

Manufacturers normally want a decent pressure for a couple of hours and then a lower pressure over a longer period.

 

[jamesmonk83]

Is the screed down?
Are you sure you got all the air out?

Manufacturers normally want a decent pressure for a couple of hours and then a lower pressure over a longer period.

No we don't plan on putting the screed down until we're sure that the pipes are okay which we're not 100% on because of the dropping pressure (original plan was putting it down this week).

We ran water through both circuits for a good 5-10 minutes until there was no air. Each circuit is around 18sqm, would that be long enough?

We spoke to the company that we purchased the kit from and they said it's fine to have the pressure at 3bar during the screeding process but that doesn't really answer/help with why the pressure is dropping in the first place (surely at 3bar it will just fall as it did at 6)?