CH Nightmare scenario

[Peter Hawkins]

Just had a plumber out to look at a CH/hot water problem. Lots of air in the system, some rads need bleeding every day, no hot water. His diagnosis is that it looks like a leak in the system, i.e you can't have that much air in without water going out. The F&E level stays fairly constant. He has turned off the supply to the F&E cistern which I will check for a day to see if the level drops. The I will turn the supply back on.

Anyway, if there is a leak its likey to be ground floor as there are no signs on downstairs ceilings or anyware else. My floors downstairs are *floating* ie, chipboard laid on a polystyrene like substance which then lies on a concrete sub floor.

So my question, which I'm almost afraid to ask, will my floors have to come up. Would the pipes be buried in the concrete or just laid under the floor boards.

Is there any diagnostics that they can you to check for leaks without destroying my entire gound floor. I know there are leak seal compounds which can be added to the system, are they any good.

I am now sh**ing myself at the possible cost of this.

All comments welcome.

Peter

[Ian Stirling]

Sorry. If the pipes are buried in the concrete (a possibility) and have not been treated appropriately, but just buried directly, which is also a possibility, there may not be any point in finding 'the' leak. As the pipes will have been corroding all along their length, and if you fix all the holes now, you're still going to need to fix next months holes.

So, if this is the case, you may be looking at replacing all the pipes.

:(

If this is the case, I'd be looking into removing skirting board, and seeing if I could put new pipes behind that, rather than in the floor, and totally ignoring old pipes, just reconnecting all the rads to the new pipe.

Routing a channel in the skirting board (in the back) could mean you'd only need a 15mm channel in the wall behind. (for 22mm) Would you be DIYing?

[bigcat]

in the system, some rads need bleeding every day, no hot water.

I'm surprised he said it must be a leak, as it could just be sucking air in at the header tank. There are 2 pipes to the header tank, if it ends up sucking air in via the one above the water line, this is what happens.

Now if you had a leak, firstly air would not get in at the leak site, since it would always be under positive pressure, so the air would only come from air dissolved in the fresh water topping up the system. With daily bleeding needed, thats a hell of a lot of top up water. IOW if it was from a leak I reckon you'd be flooded by now. So, you can stop worrying about your floor.

NT

[Peter Hawkins]

I had considered that too, I mean water exiting under from a pumped system should not allow air in. The following concern me:

1. There is NO vent pipe over the F&E cistern, just a mains in and feed to system out, so I'm not sure where the air would be sucked in.
2. Air in means water is going somewhere, the level in the F&E isn't rising, could the boiler be faulty, and boiling it off.

The system I have looks like diagram in the following link:

[Peter Hawkins]

Not DIY'ing. The boiler is in the garage, where the pipes go into the concrete they are insulated in the standard foam tubing, I assume then that this would be used throughout.

[Markus Splenius]

I'm far from being an expert, but there are devices you can get to connect your pipework to a car foot pump to do a pressure test, but that relies on you sealing the system at some point, otherwise the air will eventually just bubble up through the vent pipe. These cost around 20 quid. I'm sure other more experienced people here will comment on these.

BTW, pipe and fittings cost next to nothing, and making joints is very easy at least in easily accessible pipe. If you don't diy, labour would be the main cost I would think.

Markus

[Dave]

Markus Splenius wrote: ... snipped

That sounds like a b***dy good idea. I need to do some plumbing which will then be "built-in" before I can test it with water - it would be good to be able to do an air pressure test. Does anyone have any more info? (although I guess it's an easy enough thing to lash together) Presumably the necessary volume of air would be a problem.

[ski]

Try if possible to turn down your pump ( some have 3 settings ) If it is on

3 it can suck air into the system.

[Peter Hawkins]

The pump is already on 1.

[Andrew Gabriel]

Oh-err, this is wrong. Air will normally enter a heating system through leaks, even when the water is under pressure. Air will leak into the heating system until the partial pressure of the air in the water (or rather the individual components of air) are the same as atmospheric pressure. Due to the water in a heating system being repeatedly heated and cooled, which changes the solubility of air forcing it out of solution to collect at high points when the water is hot, as the water cools the partial pressure of air in solution will drop. There's about a factor of 2 between the amount of air which can dissolve at room temperature and at max radiator temperature, so when the demand for heat stops and the system cools down, an air molecule just outside the leak sees a 50% vacuum inside the heating system, and gets sucked in, even though the water pressure is above air pressure. Next time the water is heated up, the solubility of the air drops and it gets forced out of solution to collect at the high points again.

Now it may well be that air is collecting in the OP's system faster that it is likely to leak in when the system cools, but it certainly isn't the case that air can't leak in just because the water pressure is higher. Also, because air is very much less viscous that water, it could leak into the heating system faster than the water leaks out through the same hole.

Of course, air entering a system by any means will quickly use up the inhibitor too. This can result in corrosion and production of hydrogen to add to the gasses which collect at high points.

[John]

I once found a leak under the floor of an office block in Leeds by putting a big dose of Fernox MB1 into the system and waiting till one of the denizens reported an unusual smell.

[Set Square]

How about this?

do a cheaper one, but it doesn't have a schrader valve - so you'd have to invent your own way of pressurising the pipework. ?id=82412&p=x4&ts=29316&destination=../cat/pro.jsp%3Fid%3D82412%26p%3Dx4

[Dave]

?id=82412&p=x4&ts=29316&destination=../cat/pro.jsp%3Fid%3D82412%26p%3Dx4Thanks! I'd never thought of air testing pipework before this thread ... this illustrates one of life's big difficulties: you don't know what you don't know! (and, of course, the value of this newsgroup!)

[Lurch]

On Fri, 21 Jan 2005 17:39:22 +0000 (UTC), "John" strung together this:

I once found a leak under the floor of an office block in Leeds by lifting a floor tile to run some data cables through and found an 8' square lake!

[bigcat]

I'm a bit stuck at this point. It occurs to me it would be quite helpful to know if there is a water leak or not. If one propped up the float in the header tank and watched twice daily, it should be possible to see what happens to the water level there, whether it drops, rises or stays. But I'm not gonig to suggest that, as if the boiler ends up heating air filled pipework it could be bye bye boiler. Maybe a better idea exists.

NT

[Peter Hawkins]

I did something similar, closed the valve on the mains inlet. The level does seem to be dropping, so it does look like a leak. Was wondering if anyone has used any of the leak sealers e.g. Fernox, must be worth a go.

[John]

Did it smell of Fernox?

[Lurch]

On Fri, 21 Jan 2005 21:52:01 +0000 (UTC), "John" strung together this:

Smelt more of not been tested! It was a brand new office block with busbar power tracks screwed on the floor. (Could mention the office on a very large development and the contractors, but I'd probably better not!)