Pressure testing central heating system

FreeBear

In preparation for a new boiler to be installed (replacing an ancient Baxi back boiler), I've been replumbing the CH system and fitting new radiators. Copper is darned expensive... Anyways, finished the final bit of pipework last weekend and did an air pressure test. Was losing 1-2 psi per hour, and put it down to a leak in either the radiator tails or the gauge. Ordered a cheap hydraulic pump (£16 off ebay), which turned up late Thursday. After figuring out how to fill the system from a hosepipe, pressurised the system to 60 psi (4 bar). Held for a couple of hours before something let go, and pressure dropped by ~1 psi per minute. Mad dash to identify the leak, then drain down some of the water to effect a repair - Fortunately, it is a joint that is easily accessible, and fingers crossed, the repair holds.

Now refilled and presurised to 60 psi again. Debating on how long to leave the system under test. DIN 18380(?) says 24 hours with a pressure drop of no more than 3 psi. I'm kinda inclined to leave it at 60 psi until the boiler gets fitted next month.

nofoollikeold

1. No reason why you shouldn't leave it pressurised, but there's no real point.  Just do the standard and provided it you have no pressure loss that's all you need.
2. You will get pressure variations between night and day.  The water will expand as it heats up during the day, and you'll get a slight pressure increase, followed by a decrease as it all cools down in the evening.  
3. You were lucky to get away with air pressure testing without incident.  It's a dangerous method of testing unless you keep the pressure down to around 0.5 bar.  

FreeBear

nofoollikeold said:  3. You were lucky to get away with air pressure testing without incident.  It's a dangerous method of testing unless you keep the pressure down to around 0.5 bar.

The test sheet I'm using says a maximum of 200 milliBar (or 3 psi) for air testing. I'll not say how high I went with air, but I agree, it is dangerous and could have had catastrophic consequences if something had let go.

FreeBear

Found me an old brass pressure gauge in the garage that reads up to 150 psi. Needed an adaptor to go from 3/8" BSP to 1/2" BSP, but once that was sorted, plumbed it in. Pumped it up to 75 psi on the 12th, and watched the pressure drop slightly over the next couple of days (down to ~70 psi). No further pressure loss over the last week, so it is looking good.

Still debating whether to drain the system down before they come to fit a new boiler or to leave it pressurised.

plumb1_2

I’d test it about 3.5 bar, as that’ll be slightly above your average prv fitted to your boiler.

tacpot12

I think I would leave the system pressurised at 60psi. You will have more faith in it. 

Do you have a pressure relief valve on the system, and have you tested this? Normally they are set to 3 bar (45psi).

If it's a vented system and you have capped off the vent somehow, you need a big sign somewhere reminding you to drain the system AND open it to the atmosphere before the boiler fitters arrive.

Good luck!

FreeBear

tacpot12 said: Do you have a pressure relief valve on the system, and have you tested this? Normally they are set to 3 bar (45psi).

If it's a vented system and you have capped off the vent somehow, you need a big sign somewhere reminding you to drain the system AND open it to the atmosphere before the boiler fitters arrive.

No pressure relief valves - I fully expect one to be fitted inside the boiler.

The original heating system was open vented, but virtually all the old pipework has been removed. Once the boiler is installed, it will become a pressurised system with a normal operating pressure of 1 to 1.5 Bar (14.5 to ~22 psi).

cerebus

Never understood why people air pressure test a water filled system, firstly if anything shoots off like an endstop during the test , it could be curtains for the poor sod who gets hit in the head with it I.e. it's incredibly dangerous

Secondly air molecules are smaller than water molecules so if you get an leak during an air pressure test that same leak probably won't show up on a water pressure test 

Section62

cerebus said:

Never understood why people air pressure test a water filled system, firstly if anything shoots off like an endstop during the test , it could be curtains for the poor sod who gets hit in the head with it I.e. it's incredibly dangerous

Secondly air molecules are smaller than water molecules so if you get an leak during an air pressure test that same leak probably won't show up on a water pressure test 

Air testing is done for exactly that reason - the air test will show up any leaks in more borderline cases, and generally do so quicker than with a water test.

It's also usually easier to clean up after a failed air test than it is a failed water test.

Any pressurised system failing poses a safety risk. The higher the pressure, the greater the risk.  As an air test may give a 'fail' result at a lower pressure, it follows that done with due caution, an air test may be less risky than a water test.

The key thing is adopting a safe method of working - i.e. don't sit/stand in the potential path of something that might shoot off.  That applies whatever medium is being used to pressure test the system.

chris_n

Wouldn't like to be anywhere near a catastrophic failure at those sort of pressures. Imagine the weld on a pressed steel radiator letting go. You would have a lot more damage than a water leak. I have seen the side of a building blown out with uncontrolled gas pressure. There is a reason compressed air receivers are hydraulically tested.

FFHillbilly

chris_n said:

Wouldn't like to be anywhere near a catastrophic failure at those sort of pressures. Imagine the weld on a pressed steel radiator letting go. You would have a lot more damage than a water leak. I have seen the side of a building blown out with uncontrolled gas pressure. There is a reason compressed air receivers are hydraulically tested.

are you talking about that submersible that went missing last week or a 60psi pressure test on a a domestic heating system