Header Tank Temperature

[Stratf01]

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

 

[John.g]

Gas or oil? if the circ pump is located outside the boiler have a look at type/model and settings.

 

[Stratf01]

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

 

[John.g]

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.

 

[John.g]

Combining the cold feed and the vent will solve that problem.

 

[SJB060685]

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.

 

[Stratf01]

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

 

[John.g]

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.

 

[SJB060685]

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.

 

[John.g]

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.

 

[Stratf01]

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.

 

[SJB060685]

So the vent and cold fill are tapped into boiler flow before pump?
That valve you mention is a make shift bypass

 

[Stratf01]

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

 

[SJB060685]

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.

 

[John.g]

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??.

 

[John.g]

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.

 

[Stratf01]

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

 

[Stratf01]

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

 

[John.g]

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.

 

[Stratf01]

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.

 

[John.g]

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!!)

 

[SJB060685]

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.

 

[John.g]

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.

 

[John.g]

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.

 

[Stratf01]

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 ☺️