I have recently moved into a house that needed the radiators changed, this all went well and the system was refilled and an inhibitor was used. All was fine for 2 weeks or so, then we started to notice air building up in the system. I drained the system again and flushed the system through then refilled but 2 weeks later we are getting the air building up again. Could this be a build up of gas in the system as it is fine as soon as fresh water is used to refill? If so what action can be taken to stop it? Thanks
You need to find out if it is air (either entrained in the new water, or introduced by leak) or corrosion byproducts. You may be finding the gases given off by your radiators rusting. The gas is flammable.
You don't mention the use of inhibitors. You must use an inhibitor to stop corrosion. Some plumbers recommend not using them. This is in order to drum up business as your radiators will expire rapidly and require expensive repair.
I haven't had inhibitor in my system for 17 years and nothing seems to be falling apart yet. The boiler looked mint inside when I opened it up and although one rad did spring a leak several years ago it was only a one off thing and possibly due to a faulty weld in the first place. I'm not saying inhibitor isn't a good idea but I wouldn't agree that radiators will expire rapidly without it. Of course Sod's Law now says that as soon as I post this, every rad in the house will crumble into dust and flood me out with gooey brown heating water.
Dave Baker - Puma Race Engines
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Thanks for the reply. When I have been refilling the system I have been putting about 1litre of inhibitor in. I had a plumber who changed the hot water cylinder and installed a new 3 port valve, from there I changed all of the rads using speedfit fittings. As the boileer is only 3 years old the only old pipework (30 years) is under the flooring I feel that if it was a leak that we would hear the air as soon as the system is refilled but the system is silent for about 2 weeks before we hear any air, after this period it gets progressivly worse. Could it be that the old copper pipe needs replacing?
Does your system have a header tank for central heating - ie is it the vented type? If so check that the system isn't pumping over. This can occur in certain system "states" only. So check when hot water demand is on, heating demand is on and when both are calling for heat. This is a sure fire way to get air into your system, and there have been many posts to google for if this is the case. Check the contents of your header tank for sludge or other deposits, this can also be an indicator!
Regular introduction of air in this way will certainly accelerate corrosion and the formation of nasties.
thanks for all the replies. Phil, I think you might be onto something here as our header tank was full of slimy greeny brown sludge and the tank is only 6 months old. If I remember correctly, the plumber made it so that any air in the system would return up the pipe to the header tank where the water flows in.
Does this mean that the 3 port valve is not working as it should be or is there another problem?
I am new to this newsgroup thing but I will try and have a search through Google for more answers.
Pump over can be caused by numerous things, or a combination of factors. If you have recently had work done, did this involve a new pump? What speed is your pump set at? What speed was it set at before this recent work? Did the work done involve anything other than swap out of rads? Was a new header tank fitted? If so what is the level of water like? - the higher the level the more likely pump over will occur. Has the overflow pipe been changed? Brown stuff in the header tank does sound like pump over, but could be due to fungal growth. Recommend you try to initiate pump over by testing system in all possible load cases. Problem may be that an intermittent fault on the valve may be difficult to pinpoint. Try the detection route first and listen for water flow in the loft (if it's audible from below) when no-one has recently drawn off domestic water. Also feel temperature of header tank from time to time. This will get warm with pump over.
If you can investigate further, answer the questions above, and search on Google groups (try "overflow header tank"), you should end up with a more complete picture. This will help you and the group understand the likely causes.
In between posts I have been in the loft to play with the different settings. It seems like the pipe to the header tank gets hot when the boiler heats the hot water, although I couldn't feel a flow of warm water with my hand in the header tank.
The whole system has been changed over the last 3 years except for the pipework under the floorboards so I will have to check the speed on the pump etc. I take it number 1 is the slower speed and 3 is the fastest?
One other thing that leads me to suspect the 3 port valve might have been installed incorrectly or is playing up is that when the hot water comes on by timer sometimes there is a large bang that comes from the system.
Thanks for all the help as I feel as if I am getting somewhere with the problem.
This pipe is likely to warm up by conduction anyway when the boiler water circulates to cylinder/rads - the extent will depend on the position of vent tee relative to hot flow. Don't stick your hand under the vent pipe! If pump over occurs, that water will be hot. You should be able to expose the pipe end (take the lid off the header tank if there is one) and both see and hear pump over. Get someone to twiddle thermostats downstairs while you're in the loft. One problem can be that the pump does loads of work pushing water round many rads, so the speed is better high. However, when only hot water is called for, at high speed, the pump throws water round that fast, that half of it heads up the overflow!
Usually yes.
sounds more like boiler ignition than three way valve - perhaps someone else can comment
As I have experienced (and am still trying to resolve some similar issues) and have had much appreciated assistance from others in this group on this and other issues, it is good to be able to give back for a change.
Still urge you to google for more info, this subject has been covered frequently and by more experienced DIYers in the past.
My solution (to date) is to run at speed 2 and increase the vent pipe height in the loft space. Somehow I think I've cured the symptom rather than the route cause though. I intend to do further work on my system when I need to disturb the rooms with the solenoid valves in.
I have found that all new plumbing gasses a bit for awhile before settling down, inhibitor or not. I siuspect dissolved salts in tee water have to react and gas a bit before they get exhausted. Ther is always resdiual flux in teh pipes, and a fair amount of other crap.
Generally the copper pipe won't have deteriorated, and I agree with Phil that it would be a good idea to track down if air is being sucked in.
Do check on inhibitor quantity though. I don't know which you are using, but generally it should be what the manufacturer recommends for
100 litre system in a typical house - whatever that is. With Fernox MB-1 for example, you normally add 4 or 5 litres. Others may be more concentrated and less required by volume.
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