Hot water flowing from vent pipe into loft tank

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Hi after some advice. Just had a new pump and magnetic filter fitted to heating system due to several rads either cold or not getting up to temperature. A faulty pump was diagnosed. Rads now hot but hot water flowing from vent pipe into loft tank. The pump is on setting 1. The pump is located downstairs in the airing cupboard and is located before the cold feed and vent pipe, which from what I understand is not the best configuration, the vent pipe is more than 300mm above loft tank. Is there anyway to stop the overpumping without having to change the layout of the pipework? Thanks for you help.
 
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I'll suggest that the hydraulic resistance of your circuit is such that the new pump is just finding the path of least resistance without the neutral point being in the correct place to hold it back.

A pump will either work or not. If it was spinning, you were likely getting a normal head. Changing the pump wouldn't fix the reason for cold rads.

Was the system powerflushed when the filter and pump were replaced?
If not, then i suggest you take the rads off and hose them through in the garden. Your system may still be sludged up.

If your system was cleaned (I'd still prefer to clean the rads as above), then maybe the new pump is just too good that its now pumping over, where your other wasn't.

If you are handy enough, perhaps just replumb the FE pipe to where it should be, and clean out the rads. Your system will work much better.

It's a similar situation i had.

Best of luck. (Read my sig).
 
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Thanks for your response. The pump was in a poor state, it made a lot of noise, when the engineer inspected it was full of crud. The system wasn't power flushed, he advised that the magnetic filter should be sufficient due to the return pipe to the boiler being hot when the new pump was fitted. Could the heat exchanger be sludged up causing the pump to push water up the vent pipe? Thanks again
 
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Possibly.

Cold rads is a dead giveaway that they are blocked though.
I think your plumber should have cleaned the system.

I think this needs to be done. Either by you or a professional.
 
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when the engineer inspected it
I would say he should fix it. It is a serious problem. It could cause death it is some thing he should drop all other work to fix. There are two types of plastic header tank thermal setting and thermal plastic the latter can do this
_44346269_203tank.jpg
if over heated. OK one in picture likely more like 100°C rather than the 70°C of a running central heating system, but is still needs sorting fast.

I have seen it where TRV's have been fitted, and reduced the flow, but really even with all radiators off it should not happen, I am no plumber, I am an electrician, and I have had problems with wrong type of immersion heater fitted, or at least immersion heater thermostat, when there is solid fuel heating water can boil, so the header tank is either metal, or thermal setting plastic some call it hard plastic which kind of grates as if hard can't be plastic.

I know often the by-pass valve was not fitted in the 80's in early days of the TRV, and to be frank 12" is 1/32nd of an atmosphere so less than ½ pound per square inch so by-pass valve would likely not help, but what I am saying systems have been modified through time, and easy for some one not to realise when some thing is missing or added.
 
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Could connecting the feed to the vent fix this problem, even if the pump is before the vent? Thanks
 
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the other thing you could try is adding a chemical cleaner, such as Sentinel X400, which will cost you about £15, and circulating it for 2-4 weeks. Bale out all the mud from the loft tank, and sponge it clean, BEFORE you start. It is not as good as a powerflush, but it will loosen sludge, and your magnetic filter will catch what it loosens and circulates. After a couple of days to start shifting the loose stuff, you can turn off all the radiators but one, open its lockshield ffully, and let all the flow go through first one rad, then a second, them a third, and so on, until it has gone through every one of them at full flow, then adjust the lockshields back and just run as normal for a few weeks. I'd want to look in the filter to clean it out and see how much it collects (scrape it into a jamjar, there will be a lot a first, then it will reduce as the sediment gets captured.

At the end of the 4 weeks you ought to drain and rinse the system, and refill with a corrosion inhibitor such as X100.

This is a fairly simple DIY job, and not expensive if you can find the time yourself to bleed the radiators, bale out the mud from the loft tank, and operate the drain cock.

It might take you a couple of hours each time so a professional would do a powerflush and charge you hundreds of pounds, but the DIY method is worth a try, costs little, may make an improvement, and will not make it any worse. He was probably hoping to save you expense. But without adding a cleaner, most of the the sludge and sediment will lie where it is.

For a better job, in summer you can take all the rads off and carry them into the garden to blast through with a garden hose, after using the cleaner to loosen it. The sediment is black and will leave a permanent stain on carpets and floors. Turn the rad upside down as soon as you get it off the wall. It is not toxic, just iron oxide.
 
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On my system, the pump is after the vent pipe. Closest to the pump, and before it, is the feed pipe.

With your arrangement, you are pumping into the vent pipe. I am no plumber or heating engineer. But, if I was desperate and in a similar predicament, I would place restrictions on the vent pipe using a valve/smaller-pipe/whatever. Making the vent pipe physically peaking higher will also work. This will make it more difficult to pump into the vent pipe. I can't tell you if this will contravene any regulations.

If the radiators were cold and now warm, I wouldn't bother doing anything with them.
 
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First thing check what speed on your new pump the old pump was no doubt a 3 speed constant curve, Look at new pump instructions set on lowest speed that still works your system.
Then get pipework sorted coming from boiler you should have 22mm open vent a stort piece of horizontal pipework 150mm max 15mm cold feed then pump going down so it looks like a H.
All normal stuff when system part drained to sort pipework add flusher as per manufacturer instructions run thoroughly flush add inhibitor.
In truth when pump fitted open vent should have been checked common problem.
 
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A pump will either work or not
Unfortunately not ... a old pump can be spinning but still not supplying sufficient torque to do the job ... we call them lazy pumps.

OP .... Is the system pumping over into the F&E cistern? if so the amount of water in the cistern wont kill anyone. The example given previously would have been where a 50Gal cold water storage cistern (CWSC) was overheated by a run away hot water cylinder, certainly 50Gal of hot water could cause serious problems and danger, the little amount water that's in a F&E shouldn't.

I would place restrictions on the vent pipe using a valve/smaller-pipe/whatever
Never restrict a vent pipe, that's what's it there for, to vent, it could be dangerous if it was restricted.

Chances are you have a partially/ blocked feed and vent - and with the pump where it is - the system is running under negative pressure and typically will pump over. How clean is the system water?

Check with a magnet around where the feed and vent join the system, if there is any attraction at all in that area then the section needs cut out and replaced, only way to fix it. This is a typical piped feed and vent, see the suggested H shape, yours may or may not be the same, in this pic the pump would be flowing downwards.

th

Chances are you had a lazy pump, the new pump has restored proper circulation, hence why your rads are now working but given the pump position in relation to the feed and vent and possibly restrictions then that's probably why it is now pumping over.

It needs fixed properly by removing any restrictions due to crud in the system and the pump moved, there are no real quick fixes once the system gets to this point I'm afraid. Creating a combined feed and vent won't fix it if it's restricted.

Whoever did the work shouldn't be calling themselves an engineer (or plumber) by the way, obviously not experienced with open vented systems if you've been left like that and recommended that a mag filter would sort it all out :LOL:
 
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Thanks for your replies. Just checked the junction between feed and vent and there is a weak magnetic attraction there when I put a magnet close to it, so guess its junked up a bit in there. Not sure how the plumber will reposition the pump though, vent pipe is 5cm from external wall going straight up, then back from that's there's a 8cm pipe section to the vertical feed followed by 25cm to the pump.
And in answer, yes the vent goes to a small f&e tank in loft
 
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Without knowing how the system is piped then it's really difficult to give suitable suggestions. Are you sure the pump is flowing to the right? Check for the arrow on the pump.

Where are the 2 vertical pipes to the left heading before the bypass, is that a motorised valve nut that can be seen just at the top of the first pipe on the left in pic3 and where the black cable(s) are heading?

Presuming the feed and vent is to the right of the pump then if it is pumping to the right and those verticals do have the motorised valves on them, then it could be turned around and then pump to the left, therefore would then be in the correct orientation in relation to the pipe layout.
 
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Interesting comment about the "lazy pump".

Not sure i agree about that. You might see the performance of pumps falling over time, hence "lazy" but i would wager thats just dirt on the impeller and casing which can be cleaned easy enough. The pump will still provide a head. If the system is so bad it can't, thats a system fault not a pump fault.
Semantics i know but still.
Modern circulators are much better than the older ones. I suspect that sometimes an old pump, properly spec'd by a heating engineer to fit the hydraulic profile of a house or housing estate will be nowhere near the performance of modern variable speed units in general usage today.

Certainly, in my case, my old pump bearings were knackered and it needed replacing but the impeller showed no wear after 20 years, although it was dirty. I'd have cleaned it up if i could have. The new pump i got was the smallest the plumbers suppliers had or i could find. It blows the pants of the old one. That's not great either, so i have to keep it on speed 1.

I suspect the "lazy pump" observation is a factor of the above. A new, clean pump is going to outperform a dirty old pump when, all things being equal, cleaning the old pump would have been just fine.

Its a cause-effect observation. To me, a dirty pump isn't lazy, it's just dirty. To the observer, the opposite would be true .

The point you made about dirty fittings reflects my experiences. My (combined) FEV pipe was badly furred up, as were all the copper in the system. The Pex was clean as a whistle.
 
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