I had a similar problem. Mine was finally diagnosed as a corroded heat exchanger pipe, the coil that sits inside the cylinder and through which the heated water from the boiler circulates. This failure enabled a path between the normally closed system and the open system, the pump forcing the water up through the expansion pipe. Hope this helps.
Running water from expansion pipe when radiators on
- Thread starter J80FAB
- Start date
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jonblair said:
Many thanks for this info which may prove to be the solution to this problem
Just to make sure, your running water was definitely coming out of the expansion pipe for the F&E tank and not the cold water storage tank ?
If the heat exchanger pipe is at fault then a replacement cylinder tank is required
Is there any way of diagnosing if the heat exchanger is corroded Thanks ever so much again for your help JONBLAIR 
J80FAB said:jonblair said:
Just to make sure, your running water was definitely coming out of the expansion pipe for the F&E tank and not the cold water storage tank ?
It depends which tank is higher. If you want to check run everything with your mains stopcock off....if the level in one tank drops as it overflows from the other then it is definitely the problem.
J80fab, if you look at number of posts Bacho has penned, it would be prudent to take on board what he advises. You do not have to follow his advise but to take note makes sense.
Netaheat (by your admission)is 29 years old. Every part on that boiler is very expensive (try getting a price for the mercury vapour switch or the gas valve). The boiler has a positive pressure chamber. It has the potential to kill you.
Can you say when the boiler was looked at last? How long was the service. What was done during the service? If the boiler was looked at recently (or at any other time), were the panels examined for rust (and worst holes)?
If a system has been installed correctly following the three 'tee' rule, pump over cannot take place. The reason why the pump is pushing the water through the vent is becuse the pump finds this path to be of least resistance. This is because the pump/ feed pipe/ vent pipe configuration is wrong. Your question may well be'why has it taken 29 years to show up' Simple answer is extreme system sedimentation or blockage. Or perhaphs recent system alteration?
Netaheat (by your admission)is 29 years old. Every part on that boiler is very expensive (try getting a price for the mercury vapour switch or the gas valve). The boiler has a positive pressure chamber. It has the potential to kill you.
Can you say when the boiler was looked at last? How long was the service. What was done during the service? If the boiler was looked at recently (or at any other time), were the panels examined for rust (and worst holes)?
If a system has been installed correctly following the three 'tee' rule, pump over cannot take place. The reason why the pump is pushing the water through the vent is becuse the pump finds this path to be of least resistance. This is because the pump/ feed pipe/ vent pipe configuration is wrong. Your question may well be'why has it taken 29 years to show up' Simple answer is extreme system sedimentation or blockage. Or perhaphs recent system alteration?
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DP said:
The boiler is 29 years old & that's a fact. There's even the original tag still on it with the date being 17 November 1976 though I think it may have been installed early 1977.
I did state that the boiler was serviced 2 years ago, April 2003 to be precise. During the service the engineer even said that it was in good nick for its age/usage & mentioned that there was no rust at the rear which apparently these particular boilers are prone to suffer from.
The reason why the service took place was because the boiler 'went to sleep' - pump turned but nothing from the boiler. When the engineer turned up 3 days later to replace the fan which had been diagnosed as faulty everything worked & no repairs were carried out
Money well spent, not !I am aware the boiler may have its faults & replacement parts may be non-existent or expensive (I notice that some of the original boiler parts were manufactured in the USA & Japan
but the reliability of newer examples is also very questionable, especially if they fail after a couple of years Anyway the CH system has not been altered in the past or recently.....
ollski said:
If the F&E tank is in the loft, the cold water storage tank surely cannot be any higher
Isn't the usual set-up: both are in the loft (at the same level) or F&E is in loft whilst cold storage is sited lower down (for example bathroom) just above the hot water cistern.
J80FAB said:If the F&E tank is in the loft, the cold water storage tank surely cannot be any higher
What if the storage tank was lifted to give greater head for a shower
In reply to olski..."Just to make sure, your running water was definitely coming out of the expansion pipe for the F&E tank and not the cold water storage tank ..."
Dont know what F&E stands for, but the water was being pumped up the expansion pipe (the vent pipe), and entered the cold water storage tank from above the lid of the tank. The cold water tank i mean is the one that replenishes the cold water that you use when you have a bath for example. It is the larger of the two tanks, the other cold water tank, which is much smaller is is the one that keeps the boiler circuit replenished with water.
As far as i know, there is no way to inspect the possibilty of a corroded heat exchanger. In my case, the internal pipe got damaged when the flange nut was tightened because it was leaking. It cured the leak, but unbeknown to me, it precipitated this horrendous problem which came to light several weeks later, and no one had a clue what could be wrong. By rights, i would have also expected contamination of the hot water supply, but there was none, and i presume the leak must have started slowly, removing slowly over weeks the contamination.
Perhaps one way tofind out would be to introduce a dye into the boiler circuit and see if it appears in the hot water system.
Dont know what F&E stands for, but the water was being pumped up the expansion pipe (the vent pipe), and entered the cold water storage tank from above the lid of the tank. The cold water tank i mean is the one that replenishes the cold water that you use when you have a bath for example. It is the larger of the two tanks, the other cold water tank, which is much smaller is is the one that keeps the boiler circuit replenished with water.
As far as i know, there is no way to inspect the possibilty of a corroded heat exchanger. In my case, the internal pipe got damaged when the flange nut was tightened because it was leaking. It cured the leak, but unbeknown to me, it precipitated this horrendous problem which came to light several weeks later, and no one had a clue what could be wrong. By rights, i would have also expected contamination of the hot water supply, but there was none, and i presume the leak must have started slowly, removing slowly over weeks the contamination.
Perhaps one way tofind out would be to introduce a dye into the boiler circuit and see if it appears in the hot water system.
jonblair said:
I didn't know what F&E meant either
but it soon came to light after reading stuff on the web that it's an acronym for 'Feed & Expansion', ie. the smaller tank that feeds the central heating system. Thanks for clarifying your problem jonblair. It's a good thing I asked
My running water is not from the expansion pipe for the cold water storage tank but from the pipe for the feed & expansion tank which is up in the loft. The cold water storage vessel in our system is situated in the bathroom just above the hot water cylinder.....
If the F&E tank is in the loft, the cold water storage tank surely cannot be any higher
Wrong! If they are both on the loft floor then the level in the domestic cistern is higher than that in the heating Feed and Expansion cistern.
I don't think they were making MkII's in 1976, you may have a spare from an older model. But OK, it's oldish. There are plenty of MK1's about.
How about you tell us what the order of the pipes is after the Flow leaves the boiler?? Is the FEED on the flow pipe? It should go boiler > vent > feed > pump, but other configurations were common, such as the Vent coming straight off a separate tapping on the boiler.
If the original installation was a bit marginal it's quite common to find that a bit of a blockage causes problems.
Easiest way to check for a leaky hw cyl coil is to note the levels in the loft , overnight, with everything cool and supplies turned off. If the lower level rises, you found it.
ChrisR said:
The quality control tag is dated 1976 & belongs to the boiler. The front panel on the boiler clearly says 'Potterton Netaheat 10-16 Mk II'.
Looks like a slight misunderstanding in the thread. By 'higher' I meant the height of the actual tank & not the height of the level of water
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