Leaky central heating pipe

[Steven]

I have a leaking joint (water) on the combi boiler, I thought I could get away with a quarter turn to get it tight again. What I have managed is to make it worse. I think any corrosion or what it was was helping keep it getting too bad.

I believe the olive has failed, I can repair this but can someone confirm that turning off the water inlet to the boiler and opening the taps will empty the tank allowing me to fix the joint. I have read the manual and from what I can make out it should be that simple. The last time I did a fix it was on a storage tank and just turned off the stop cock.

 

[NetBlindPaul]

You'll probably need to shut the boiler down eletrically to ensure it can't fire up when being repaired.
Isolate the water supplies to the boiler.
Drain down.
Fix the leak, you can get olive pullers though you need to be sure that is the issue.
Then refill and repressurise.
Then recommission the boiler basically.
Not difficult really.

 

[Steven]

Thanks that is what I expected. There is no water above the nut so I expect that the olive failed and hopefully nothing else.

 

[Eric The Viking]

Which side is it on - CH or domestic hot water(DHW)?

Olives don't 'fail' in my experience, although if the joint is made badly or overtightened the joint may leak.

If it's CH it should be about 1bar - 1.5bar, depending if you have a pressurised or open (header tank system). If it's DHW it may be more, but shouldn't be above 3bar really.

When you redo the joint check the pipe hasn't been 'waisted' where the olive was through over-tightening. If it's no longer cylindrical but squashed in, you'll not easily get it to seal as-is, and if you do it may start leaking again later. Best to cut the end off and replace with fresh pipe.

I _never_ use PTFE tape on compression (olive) joints, but use Bosswhite (put it only on the pipe and the end of the olive facing into the fitting, keep it off the threads), and sometimes PTFE 'toothpaste'. Also these spanners are reasonably cheap and really good - there's nothing more annoying in an awkward space than fiddling with an adjustable spanner that keeps coming loose.

I have the brass wind-up type of olive puller. It works well, but only when you can get good access to the end of the pipe. Previously I could only cut the olive almost through with a hacksaw, as close to parallel with the pipe as poss., then snap it off with a sharp twist of a biggish screwdriver in the kerf. If you do this, be careful not to scratch the pipe, as it won't seal later.

HTH,

E.

 

[Ateallthepies]

I have a leaking joint (water) on the combi boiler, I thought I could get away with a quarter turn to get it tight again. What I have managed is to make it worse. I think any corrosion or what it was was helping keep it getting too bad.

.

You won't have a tank if it is a combi boiler surely?

Steve.

 

[Eric The Viking]

You won't have a tank if it is a combi boiler surely?

Steve.

You shouldn't have a DHW header tank (big), you may have a CH header tank (small), and you shouldn't have a hot tank, obviously.

I've seen some odd things though.

E.

Edit: don't over-tighten compression fittings either. Those spanners I mentioned are big and can exert a lot of force. If you do squash the pipe it will leak and never seal well. Frankly, this sounds like what the original plumber did. I had to remove tiles dig back into the wall and re-plumb a shower because the apprentice did it, and overtightened both hot and cold fittings. He wasn't taught well!

 

[RogerS]

Don't agree with Eric re PTFE tape. It's always worked well for me. Trying to get the olive off - especially if the pipe has been deformed - is a recipe for disaster.

Re 'shouldn't have a DHW header tank'...you can get combi's designed for vented systems now.

 

[Steven]

The fault is on the DHW I have sorted out some spare olives and spare pipe to replace the section with PTFE and bose white to hand if required.

Also how often should you expect to top up the CH system, I filled it to 1.5bar about 3 weeks ago and it is down to 1.1 today.

 

[NetBlindPaul]

You have a leak somewhere!

 

[Eric The Viking]

Don't agree with Eric re PTFE tape. It's always worked well for me. Trying to get the olive off - especially if the pipe has been deformed - is a recipe for disaster.

Re 'shouldn't have a DHW header tank'...you can get combi's designed for vented systems now.

In the house I have now, I have dealt with three leaks caused by PTFE tape incorrectly applied to compression fittings (by other people). It is incorrect use and will cause premature failure if the pipe is subjected to movement, such as temperature expansion/contraction.

If the pipe has been waisted because of over tightening, you won't get a reliable seal unless you replace it.

Also how often should you expect to top up the CH system, I filled it to 1.5bar about 3 weeks ago and it is down to 1.1 today.

I'm with Paul on this one - you have a leak somewhere.

It's possible your pressure relief valve is leaking. It's on/near the boiler, often with a red plastic cap, and it vents to the outside air, usually through a 15mm pipe. Look for drips. My Vaillant ( :evil: ) has the thing mounted upside down, in such a way that the stub of pipe going to it fills with rubbish, which then stops the valve from sealing properly if it's ever opened, for example to drain down the system to do work on it.

The other boiler favourite is the 3-way diverter valve that does the DHW heating. They can be refurbished/repaired/replaced, but it needs a specialist (you're not supposed to work on stuff inside the boiler if you're not 'competent' in the terms of the regulations).

There is an expansion vessel, usually inside the boiler on smaller systems, that allows the water in the CH to expand when it heats up, instead of the pressure fluctuating wildly. These sometimes lose pressure (there is a Shraeder "tyre" valve on them usually). Setting the correct cold pressure is a job for a plumber, but if it's lost pressure and you fill the system, the pressure will fluctuate wildly, as the expansion vessel fills too and there's insufficient space for hot water to expand into. In that case, it usually goes up when the system is hot and down again when it's off (CH, not the DHW mode on its own). They have an internal diaphragm to keep water and air separate: this occasionally perishes, but usually it just goes down over time like an unattended tyre and a simple pump-up to whatever the right pressure is sorts it out (job for a plumber, but should only take minutes really).

If not in/near the boiler, look for crusting/leaking around radiator fittings (most common problem). If you're losing 0.4 bar over that time, it's not a tiny leak, so you ought to be able to see it.

To be honest, it does sound like you need a pro to take a long careful look at the system.

 

[Steven]

I have not seen any leaks other than the one on the DHW, I can not see any marks on the rads and all my pipe work is above the floor behind some boxed skirting (Concert floors and walls). What kind of volume of water would expect to see if there is a leak.

I did notice today that the pressure is lower again 1bar with the CH off at the moment, I will look at it again tonight when it is on. Is there a correct time to top up the system i.e CH off or on?

I received some names for a plumber and Gas safe man last night, I always like to do my own work if I can even if it does mean getting it passed in the end.

 

[Eric The Viking]

Cold system for filling, otherwise the pressure reading is unreliable.

Regarding the pressure drop: 1bar upwards cold ought to be OK for the CH pressure (don't go above 1.5bar cold). Have you looked outside for dripping from the safety valve's pipe? You can also get automatic air bleed valves failing to seal (on the pump, for example). If there are signs of rust in the bottom of the boiler casing, it may be that - the leaked water will evaporate when the boiler gets warm.

You can tell if the expansion vessel is not doing its job fairly easily:

Make sure the rads are well bled of air/gas first, and any air release valves bled too.

Drain off some circulating water so it's down to about 0.5 bar, then refill, watching the pressure gauge as you go. If it's working, the pressure will rise as you fill the system, then stay approx constant once you hit the operating pressure (you're then just compressing the air in the vessel's bladder, at least for a bit). If it goes up steadily, fairly quickly and smoothly above about 1.5-1.75 bar without seeming to hit a 'shelf', the expansion vessel probably isn't holding air pressure.

You can only properly check the expansion vessel with a pressure gauge, when the system is de-pressurised. They're usually pre-charged to around 1bar, depending on manufacturer and the vessel's volume.

This is all stuff your plumber ought to do, really, as it's hard to diagnose without taking the cover off the boiler.

If you're having to re-fill the system that often, I'd worry on two counts: (1) you do have a leak somewhere inside the boiler or elsewhere, and (2) you're diluting the system inhibitor (corrosion proofer), which will allow the rads, etc. to corrode. If you get a lot of gassing from radiators, etc, this is a sure sign that's what's happening.