Cold Rads and header tank overflowing

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Rusty Stains

The problem started when the overflow pipe from the header tank started pouring down the exterior walls of the house. We'd had a new boiler installed and the system flushed so the overflow left a dark red streak down the wall.

Called back the plumber to try and fix the problem his solution was to construct a 5 meter run of copper piping around the loft to somehow (god only knows how) stop the overflow. Obviously it didn't work and we just got hit with the bill. The leaking continued until last summer, then stopped.

We cleaned up the staining and thought the problem was over, until this winter when the heating was on full blast for 16 hours a day. The overflow started again, this time with a vengeance. Called in another plumber who just shook his head and said he didn't know what was causing the problem.

Does anyone have any idea what might be causing this please? The only other thing that is odd in the heating system is that 2 of the radiators on the top floor need a total bleeding every 3 weeks or so- they seem to be about 80% full of air. This obvioulsy affects all the rads on that floor so unless they are regularly bled the heating is pretty minimal up there.
 
construct a 5 meter run of copper piping around the loft to somehow (god only knows how) stop the overflow
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Sounds like a bodge up.

Sounds like the system is overpumping - The pump may be set too high or the pipework may not be configured correctly.

Also if you have been constantly losing water your rust inhibitor will have been lost and the radiators and boiler will have started to corrode which will be eating away at the metal and clogging the system. The air in the rads is either air drawn in trough the vent pipe caused by the incorrect configuration (sucking from the tank and blowing out the vent pipe). Alternatively it could be hydrogen from the rusting of the radiator.

Was the water being blown out when the heating started up or when turning off?

Check the setting on your pump and if possible try it on a lower setting. How high is the vent pipe above the tank in the loft. If it isn't high enough it may be adding to the problem.

If it's a pipework configuration fault, it may be possible to cure i by disconnecting the tank and fitting a pressure vessel system instead, but your system needs to be leak free.

What kind of boiler did you have before and what do you have now? Do you have two header tanks in the loft - a large and a small one?
 
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It really was a bodge job. I'll turn down the pump speed and see if that helps. Thanks for that.

Not sure when the water was blown out at all. It never happens when I am outside waiting for it to happen. There's a very good chance that the piping isn't configured correctly as well. Looks like the original system had additions tacked on, complete with different diameter piping!

There are two tanks in the loft. One for the hot water feed and one for the heating. Just went up there to check and the heating tank is full of orange gunge.I'm not sure what pipe is the vent pipe but there is an J shaped pipe hoovering over the heating header tank - probably about 3 inches from the waterline - this is then attached to the 5 meter pipe loop.

The old boiler was condemned by British Gas so we were forced to take it our when we moved in.It was from about 1984. The new one is a Potterton Derwent compact about 4 years old.
 
If your tank is full of orange gunge then the system will have gotten very badly corroded due to loss of inihibitor and addition of fresh water. Will probably be sludged up.

I would recommend you get a REPUTABLE plumber to take a look.
 
The Derwent Compact is a commercial boiler, minimum output 50kW. How big is your house? How many radiators do you have?

The average house will only need a 15-20kW boiler.
 
There are 19 rads in the house over three floors .The boiler installer insisted we needed an commercial boiler... I know...

The installer had all the right credentials - Corgi registered but we realized, too late that we'd been played. So do you think that the air in the top floor rads is somehow linked to the gunge? I was thinking that maybe replacing the two offending rads (they are really ancient) might help solve the problem.
 
changing the rads is unliklry to solvr yout problems you need to get the system looked at almost certainly the cold feed and vent are positioned wrongly allowing air to enter the system sealing the heating may be a way out but your gonna need a very big exspansion vessel
 
With a system that size it could be just that your expansion tank in the loft is woefully undersized to take the volume of expansion without it overflowing each time. How big is your expansion tank? The natural water level may be too high - when cold it should fill to a couple of inches above the outlet, leaving lots of room between the level and the overflow to take expansion.

You're going to need the system flushed as it will be gunged up. You only need to change radiators if they are badly corroded - if rust spots have started to appear on them as the metal gets eaten through.

Probably the easiest way to fix is making it a sealed system but you need a big enough expansion vessel.
 
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WHPES is right get the system converted to a sealed system.

The cause of the overflowing is either pumping over or inadequate room for expansion. Explanations:

1) Pumping Over. Due to an incorrect installation the system pump is pushing water up the feed or vent pipe resulting in water being pumped into the header tank. It is pumped in faster than it can drain back into the system so the header tank will overflow.

2) Expansion. When the water in the heating system is heated from cold it will expand (3 to 4%). This expansion has to be accommodated. In an open vented system the vent pipe should be sized to take the expansion without overflowing into the header tank. When there is a problem the vent pipe is not big enough and so will overflow thus the header take will overflow. One of the plumbers has put in a loop to increase he volume of the vent pipe to try and stop this happening but this will only work if the loop is above the fill height of the header tank.

Now the bad news: When the header tank overflow water is lost from the system which will then be made up when the system is off. This new (make up) water will contain lots of oxygen thus you now have ferrous metal, water and oxygen together which will result in corrosion. Your radiators and boiler are in danger of failing and the system will be sludged up and need cleaning.

I would do the following:

1) Have the system powerflushed.

2) Convert to a sealed system.

3) Add system inhibitor

4) Hope that the corrosion is not so bad that radiators start leaking.
 
f and e tank is undersized. fit a larger one- probably put a standard one in place when he put it in....

powerflush and remove the 5 metre loop he put in - he put this to compensate for the large amount of water expansion.... bodged job! i would personally get him back and ask him to explain why he put a 5 metre loop in instead of measuring and assessing for a new f and e tank as he should of done, when he cant explain tell him you would like it done properly, a feed and expansion tank properly sized and fitted and would now like a power flush to clean the rads and that he had better hope that the rads havent corroded.... i would be saying this to the plumber who fitted the system and the plumber who ran the 5 metre loop. both have not done there job properly, and the other plumber who came and didnt have a clue should of know also shouldnt be calling himself a heating engineer.

i for one am fed up of so called plumbers and heating engineers not knowing the basics about installing systems but still seeming to get the work... do we blame this on the customers chasing cheaper prices or the cowboys jumping into our trade...
 
Thank you all for this help. The expansion tank is really small - was there before and not replaced by the person who installed the new boiler. We tried getting him back to put the job right but he just refused - because the house was falling down around us we just moved on and got on with the restoration. This guy wasn't the cheapest by a long way but he was the only person Corgi registered to install commercial boilers. We have since found out that he is a well known cowboy.

One more question if I may - how could our heating system be converted into sealed system?

Also - any Central Scottish heating engineers out there please?
 
You need to get a reputable plumber in to do it. It requries someone who is certified to install unvented systems. It has to be done correctly or it could be dangerous.

The tank is removed and a pressurised expansion vessel (a metal bottle containing a rubber bladded which is squashed as the water expands into it. It is placed in the heating circuit. It has a safety valve on top, a pressure gauge and filling loop connected to the mains. No one can tell exactly how it can be done without seeing it.

BTW Corgi has been obsolete for the past year - it has been replaced by the Gas Safe Register.
 
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Nineteen rads fed from a 50kW boiler!

It may be a bit late now, but you can find out what size boiler you really need by using the Boiler Size Calculator. You can then compare this to the total output from your radiators (assuming they are steel ones) by using the Stelrad Elite Catalogue.

Which pump do you have? The standard 15/50 and 15/60 are not big enough to provide the necessary flow rate for that size boiler.
 
I did the calculation and it said that I needed a 40 kW boiler. We are in Scotland and the house is ancient - can't use cavity wall insulation etc etc. I don't think the pump is the problem as the heat circulates pretty well. We got a different heating engineer to put that in because the original one did not push the heat above the 1st floor. I've just called a local-ish heating engineer who I've avoided i the past because he never turns up but is supposed to be OK.

Thanks again for all the suggestions. I'll be armed with information, if the heating engineer ever turns up.
 
WHPES said:
You need to get a reputable plumber in to do it. It requries someone who is certified to install unvented systems. It has to be done correctly or it could be dangerous.

The tank is removed and a pressurised expansion vessel (a metal bottle containing a rubber bladded which is squashed as the water expands into it. It is placed in the heating circuit. It has a safety valve on top, a pressure gauge and filling loop connected to the mains. No one can tell exactly how it can be done without seeing it.

BTW Corgi has been obsolete for the past year - it has been replaced by the Gas Safe Register.
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are you saying you need unvented to install a sealed system?you only need unvented for cylinders
 
sealed heating circuit doesnt need unvented - but if your installing unvented hot water it does - either way he's best off getting someone who knows what theyre doing.

by the sounds of it i might move up there haha only half decent plumber doesnt turn up lol.
 
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Im only fairly new to this game, (about 2 years now) but surly hes only saying to pressurize the heating side of the hot water cylinder, not actually pressurize the DHW inside the cylinder for which you will need a plumber with an unvented ticket. If it was the case then unless you have an unvented ticket you could not fit a new system boiler that works on a sealed system! Hope Im right and havent made a total fool of myself!
 
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