Search the forum,

Discuss Header Tank Temperature in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

Messages
42
Just been in loft and noticed header tank on my vented system is hot. I understand that this acts as a feed for heating and expansion when heating water gets hot.
Is this normal for tank to get very warm?

Both the feed pipe and vent pipe are hot but no water coming out of vent.

Never noticed before and had no work done recently although I have a suspected 2 port valve issue as hot tap water always very hot despite no hot water is active. Also waiting on getting a system flush as have hydrogen in rads.

Heating after bleeding works well.

Any thoughts or suggestions hugely appreciated

Thanks
 
It's oil.
Pump is a grundfos set on lowest setting. Not sure on other specifics of pump.

Vent pipe is 22mm and feed 15mm about 3 meters above pump.

Thanks
 
If the circ pump is on the boiler flow (outlet), then from the boiler you should have the Vent then the cold feed within 6 ins of it and then the pump. If the pump is located on the boiler return then feed could be teed in somewhere else. Problem possibly due to blockage where the cold feed is teed in to the system.
I see that both vent&cold feed are hot so unlikely feed blocked, this problem may be there for years if you are getting corrosion/hydrogen from your rads.
 
Last edited:
Its not uncommon for heat to drift up the two pipes, copper is an excellent heat conductor.
Ideally the cold fill will drop below the boiler flow and then u bend back up into it to prevent as much rising as possible.
If the two port is stuck open then the only thermostat governing the HW temperature is the boiler thermostat. If you have a multimeter and are competent this is easy to confirm. In the mean time you could turn your boiler stat down slightly to reduce the stored water temperature.
Hydrogen in heating systems is a by product of the oxygen in the system reacting with the iron content of steel radiators, which causes the accumulation of sludge. A powerflush will help but you need to get to the bottom of the air ingress as well.
 
Its not uncommon for heat to drift up the two pipes, copper is an excellent heat conductor.
Ideally the cold fill will drop below the boiler flow and then u bend back up into it to prevent as much rising as possible.
If the two port is stuck open then the only thermostat governing the HW temperature is the boiler thermostat. If you have a multimeter and are competent this is easy to confirm. In the mean time you could turn your boiler stat down slightly to reduce the stored water temperature.
Hydrogen in heating systems is a by product of the oxygen in the system reacting with the iron content of steel radiators, which causes the accumulation of sludge. A powerflush will help but you need to get to the bottom of the air ingress as well.
Thanks for the input.
Air ingress is an issue I have have had for a long time.
The automatic air vent is situated after the pump close by but never worked so recently I have bought I different type with the hopes this will resolve the issue.
There is no sign of water anywhere in the visible system from what I can see.
Is there a fairly simple method that can be used to detect where air is getting in. 🤐

Thanks again
 
Can you give some idea of location of the pump (flow or return) and the locations of the vent & feed (or a sketch) because if installed or re installed correctly you will not get any air ingress.
 
A sketch of system layout will help a bit further.
Air can be drawn into the system through venting over, it can be added to the system if constantly topping up ie a leak hidden somewhere, or frequent drain downs etc. If parts of the system are under negative pressure this can draw air in, or pull dissolved gases out of solution.
In a properly designed and executed install air should not be entering a system.
 
Go to page 17 of glowworm.pdf for the VCP system, the very simple combined cold feed and vent is mine from its installation almost 50 years ago and works to perfection, no air ingress, some of same rads for > 40 years.
 

Attachments

  • hxi_glowworm.pdf
    3.3 MB · Views: 7
  • Combined Cold Feed & Vent. rev1.JPG
    Combined Cold Feed & Vent. rev1.JPG
    36.9 KB · Views: 10
Hope this makes sense.
One thing I noticed is that the return flow from tank has a pipe going to flow side of pump with isolation valve open? Surely that can't be right can it? 🤔
Thank you guys and thank you again.
IMG_20201230_213610.jpg
 
So the vent and cold fill are tapped into boiler flow before pump?
That valve you mention is a make shift bypass
 
So the vent and cold fill are tapped into boiler flow before pump?
That valve you mention is a make shift bypass
Ah sorry I forgot to add cold fill and vent.
Yes both are tapped in immediately before pump. Below is ammended sketch.
So should this valve in bypass be closed??

Thanks
IMG_20201230_220450.jpg
 
That valve should be open about a quarter of a turn. When the TRV'S start throttling in the pressure can increase, this bypass allows water to flow back to the boiler without the pressure increasing and causing noise at the rads. On older systems it was also used to divert hot water back to the boiler to prevent back end rot on standard efficiency boilers. Is yours a condensing boiler?
Your ammendment suggests the vent, cold fill and pump are situated as they should be and a positive pressure will be maintained throughout the system and air should not be drawn in.
 
Isn't this the famous VCP?? and if close coupled (less than 150 mm ??) should work OK, except there is a restriction between the two??.
 
That valve should be open about a quarter of a turn. When the TRV'S start throttling in the pressure can increase, this bypass allows water to flow back to the boiler without the pressure increasing and causing noise at the rads. On older systems it was also used to divert hot water back to the boiler to prevent back end rot on standard efficiency boilers. Is yours a condensing boiler?
Your ammendment suggests the vent, cold fill and pump are situated as they should be and a positive pressure will be maintained throughout the system and air should not be drawn in.
Just saw your post, so unless either a big distance between the two or a partial blockage??, a very small restriction here will cause havoc because the atmospheric pressure is acting on a area hundreds of times bigger (F&E tank) than than a 3/4 ins vent, I've always preffered the combined cold feed and vent because it destroys the U tube imbalance effect.
It looks like the hot water is going up the vent (maybe with pump start/stop) and back down via the cold feed......disaster.
 
That valve should be open about a quarter of a turn. When the TRV'S start throttling in the pressure can increase, this bypass allows water to flow back to the boiler without the pressure increasing and causing noise at the rads. On older systems it was also used to divert hot water back to the boiler to prevent back end rot on standard efficiency boilers. Is yours a condensing boiler?
Your ammendment suggests the vent, cold fill and pump are situated as they should be and a positive pressure will be maintained throughout the system and air should not be drawn in.
Yes a condensing boiler.
Thanks for input
 
Just saw your post, so unless either a big distance between the two or a partial blockage??, a very small restriction here will cause havoc because the atmospheric pressure is acting on a area hundreds of times bigger (F&E tank) than than a 3/4 ins vent, I've always preffered the combined cold feed and vent because it destroys the U tube imbalance effect.
It looks like the hot water is going up the vent (maybe with pump start/stop) and back down via the cold feed.***..disaster.
Thanks for the pointers.
The vent and feed and pump are close together say within 120mm.
So how would I prevent hot water going up the vent? Just by combining the cold feed and vent?

Thanks
 
Is (are) the distances between the vent and feed small and also between the feed and pump?, if so then suggest ensuring no restrictions whatsoever in this area, maybe involves cutting out and renewing that whole section as this is a proven way of installation and must work well normally.
 
Is (are) the distances between the vent and feed small and also between the feed and pump?, if so then suggest ensuring no restrictions whatsoever in this area, maybe involves cutting out and renewing that whole section as this is a proven way of installation and must work well normally.
Thanks again.
Yes they are close together.
Trouble is this is in a really stupid location. Almost impossible to get to 😞
Here's a photo.
IMG_20201230_225740.jpg
 
Thanks for the pointers.
The vent and feed and pump are close together say within 120mm.
So how would I prevent hot water going up the vent? Just by combining the cold feed and vent?

Thanks
120 mm is supposed to be quite adequate. You could consider combining them, mine is as shown but my pump is on the return to the (OF) boiler, don't think this should make any difference though. (Ignore pic on left!!)
 

Attachments

  • IMG_20200708_085158 rev1.jpg
    IMG_20200708_085158 rev1.jpg
    104.8 KB · Views: 12
  • IMG_20201230_220450 Rev.1.jpg
    IMG_20201230_220450 Rev.1.jpg
    401.2 KB · Views: 10
Last edited:
Just saw your post, so unless either a big distance between the two or a partial blockage??, a very small restriction here will cause havoc because the atmospheric pressure is acting on a area hundreds of times bigger (F&E tank) than than a 3/4 ins vent, I've always preffered the combined cold feed and vent because it destroys the U tube imbalance effect.
It looks like the hot water is going up the vent (maybe with pump start/stop) and back down via the cold feed.***..disaster.

This is still an area I'm researching but the point the feed enters the system is like the point of no pressure change on a sealed system. Whether there's a restriction or not on the suction side the pump suction pressure will not change, regardless to whether the pump is running or not. Since the pump suction cannot change the pump discharge must change when the pump energises. This DP must show as a positive increase at the pump discharge.
 
Thanks again.
Yes they are close together.
Trouble is this is in a really stupid location. Almost impossible to get to 😞
Here's a photo.
View attachment 46950

Presume the vent is attached to the pump inlet pipe??.
I would suggest just draining down the system sufficiently to remove and blank the cold feed connection, leave that plastic pipe, then remove it at the header tank and T the cold in to the vent with a compression T, you can always revert if any problems.
Or mybe when you drain just ensure no blockage/restriction where you remove the cold feed.
 
This is still an area I'm researching but the point the feed enters the system is like the point of no pressure change on a sealed system. Whether there's a restriction or not on the suction side the pump suction pressure will not change, regardless to whether the pump is running or not. Since the pump suction cannot change the pump discharge must change when the pump energises. This DP must show as a positive increase at the pump discharge.
Probably correct but if there is the slightest difference between the "suction" pressure at the vent and the cold feed connections then a problem, the main reason for having these so close together is to destroy the U tube effect but still allow free venting.
 
Presume the vent is attached to the pump inlet pipe??.
I would suggest just draining down the system sufficiently to remove and blank the cold feed connection, leave that plastic pipe, then remove it at the header tank and T the cold in to the vent with a compression T, you can always revert if any problems.
Or mybe when you drain just ensure no blockage/restriction where you remove the cold feed.
Sounds like a good plan that!
I can't thank you all enough for the advice .
Thank you ☺️
 
The reason for having vent and cold fill a maximum of 150mm apart is so they're both in the neutral zone. From the picture they look further apart. Its possible the system is venting over.
 
Just been in loft and noticed header tank on my vented system is hot. I understand that this acts as a feed for heating and expansion when heating water gets hot.
Is this normal for tank to get very warm?

Both the feed pipe and vent pipe are hot but no water coming out of vent.

Never noticed before and had no work done recently although I have a suspected 2 port valve issue as hot tap water always very hot despite no hot water is active. Also waiting on getting a system flush as have hydrogen in rads.

Heating after bleeding works well.

Any thoughts or suggestions hugely appreciated

Thanks
Your correct in that the feed and expansion tanks act as
1, A way of filling the system ,beit heating or hws
2,A way for the system to breath and or expand
Your description doesn't say if your tank is heating or pottable water
My assumption is that your talking about the heating, although you do mention excessive temperatures in the dhws ,Does the header tank have separate feed and expansion or is that pipework combined ? It sounds like you have a "S" type heating system this is where you have 2 or more 2 port valves and 1 heating pump, traditionally heating systems of this type were normally configured pumped ch and gravity fed hot water, normally heated via a back boiler and fire front situated in the lounge, this means that the pump only comes on for the CH ,the dhws is satisfied via gravity ,in that the boiler fires for dhws based on the temperature being lower than its set point,as we know heated water rises and cooler water falls this continues until the thermostat is within 3 degrees +/- 2 degrees.
Heating water for your hot water cylinder was given to you as a bye product of having the heating on,say during winter , the pump would push open a none return valve and heating water would flow through your cylinder until its set point was satisfied
Later installations and better installations practices allowed for what we call "fully pumped" systems, this is where the pump runs for both heating and hot water ,the pump would be switched on when the 2 or 3 port valve actuated to its end stop ,pushing on a microswitch this would send power to the pump and boiler switch live, providing your roomstats setpoint was low enough this would start the ignition sequence and fire the boiler and the pump would circulate water until the set point was satisfied if the roomstat was satisfied the pump will continue to run until it falls below that set point, if however the overheat stat switches off the boiler the live supply is blocked and the pump stops ,this is where your problems start your system is what we call venting over ,essentially the boiler is staying on for a period without the pump the water gets too hot and overflows into it expansion tank ,the problem you have is
1, Why is your pump not working
2, Why is the boiler staying on
Your engineer needs to assess your heating system and check its sequence of operation to see at what point its failing ,this is why proper engineers wont give advice over the phone, because guessing causes accidents,
If nothing else your now wiser in heating and heating systems
Hope this helps 👍🏼
Ps Hydrogen gas in a heating system ,again is a bye product of germs of an organic matter have died ,decomposed and produced the gas ,venting the radiator or radiators will emit a smell like a wet fart but joking apart can be quite dangerous and your right to have it removed ,flushing the system will of course remove all matter and decomposition but more beneficially will replace old water for new water this exchange of water should actually be done every 3-4years this will again remove and debris and allow for correct cleaning and the installation of inhibitors these chemicals will slow the production of sludge and excessive pump and valve wear and tear extending the lifespan of the system, you could go a step or 2 further by adding in during the drain down a magnetic particulate filtration device, this will catch large and small down to 3 microns products which left to circulate will eventually block radiators and boiler heat exchangers now your being proactive and that's a good thing
 
All my design guides, college text books, CIBSE heating design etc state a maximum of 150mm. Obviously anything within this distance is acceptable.
If the OP fires the boiler up today whilst he's in the loft he will be able to confirm if it is venting over, if it is then I think we've found our problem.
 
It might be advisable to be in the loft and get someone to start the boiler as it may only be venting on pump start up or stop.

What could the cause be, SJB, IYO, if venting, since distances well within limits?
 
Looking at the image John i can't say that is within limits. One would have to get a ruler out and measure centre to centre. If it is within limits then technically pumping over shouldn't occur.
 
The bit I can't see properly is where (if) the vent is actually coming off the pump inlet just below the cold feed T which is quite clear, it might look as if it does going by the 2 Ts very close together, if everything as it should be then hard not to conclude that no restriction somewhere?.
 
Ah, I apologise. I was looking at the image wrong. I thought the vent was the vertical 22mm on the left. If its as you suggest then should be within limits.
Just so I'm on the same wave length as you John, how are you thinking a restriction is causing potential pump over?
 
I'm thinking of some restriction/build up between the vent and the cold feed because even though very short at ~ 120mm might cause some venting, you wouldn't really know except you removed that whole piece, combining the two as I suggested might be a easier way out.
Only other thing I can think of is very improbable, that the pump is pumping the wrong way.
 
I can see where you're coming from mate but I cant see how a slight restriction would cause the pump to vent over, seeing as the vent is within the neutral point of the systems margin. Of course I could be wrong.
To the OP. Is it hydrogen forming in the system, or hydrogen sulphide? The formation of the two happens for different reasons.
 

Reply to Header Tank Temperature in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

Creating content since 2001. Untold Media.

OFFICIAL SPONSORS

OFFICIAL SPONSORS

Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock