More air in radiators.

[MickBrown]

Customer has a problem with a lot of air in an upstairs radiator which needs bleeding everyday. I checked for leaks and also did a check for gases from corrosion, non could be found. I have inserted a plan of the system, the water is heated by a multi fuel stove with gravity hot water and pumped central heating. The 2 x 15mm tails at the bottom are a later addition of 3 radiators on a 2 pipe system, upstairs it changes to a 1 pipe system and the air collects in radiator 1. I suspected that air was being drawn from the vent and circulated and gathering in radiator 1. I turned the pump around and although I got pumping over in the f/e tank there is now no air in the system. So my theory seems to hold some credence. If I put an automatic air vent at point 'X' do you think this will solve the problem.

 

[dancinplumba]

what would happen if you capped off vent on pump return ? why does it have two vents ?

 

[PlumbBobBob]

why does it have two vents ?

i was wondering that as well

 

[dancinplumba]

could be when refilling it a path for the air out of rads. cuold put manual vent there

 

[PlumbBobBob]

no i think he just hasn't drawn the other tank for the hot water as he says it's gravity hot

 

[Best]

Yes, try a manual vent & see how it works. Don't use an auto vent as they can draw air in on suction side of pipework! And not needed for a rad circuit, & they leak often.

 

[REDSAW]

pop a auto vent on rad 1..?

 

[diamondgas]

Why turn the pump around in 1st place mickBrown?

As said, do away with the vent of the heating side as it may be drawing down there? Is the cylinder primatic or indirect? Also could try running the pump on a lower setting if possible. Pumps on the return can place the system under 'negative' pressure and in the worst case draw air in through connections! IMHO

 

[MickBrown]

Thanks for the replies.

I turned the pump around as the customer said the air in the system had been happening for 2 or 3 years and then they said they had a new pump around 3 years ago. I was thinking air was being drawn down the vent and if the pump was originally the other way around then and when it was changed it was fitted the wrong way then this seemed logical, also there was red tape on the pipe so I thought it was the flow side. When I saw the pumping over I knew something was wrong, so I did some more investigation and discovered it was the return side. When I talked again with the customer I found out he put the red tape on as there was a pipe clip there and the pipe would not stay in the clip so he put red tape on hopeing it would jam in the clip better. When I siad to him that it seemed strange that this problem had only been happening for 2 or 3 years since the changing of the pump his wife said (who was not there earlier) "no it's been happening a lot longer than that"! So it was a little being misled along with my inexperiance that caused me to turn the pump around. Anyway on the up side no air was drawn in to the system during the period the pump was on the wrong way round.

Going on to some of the recommendations. I thought of an auto air vent on the rad, however it is in the main bedroom and there is so much air being drawn in to the system it could be going off when they are in bed (being a stove it takes time to cool and stop the heating process).
With the suggestion of a manual vent, would this just move the bleeding of the system from the rad to the manual vent? There is so much air (it takes about 1 minute per day to bleed the rad) then the manual vent would need bleeding every day.
I like the idea of capping off the vent, It seems logical that although there is 2 seperate circuits there is one lot of water that mixes in the boiler. The vent is basically for the water in the boiler in case it over heats so one would be sufficient.
I am fairly certain the HWC is indirect and not primatic as there is an F&E tank, if it was primatic then there would not be an F&E tank.

 

[dancinplumba]

if you put manual air vent instead of vent you would only open it when filling system, and no air is the being drawn in so no more bleeding ???
you could put aav where you said if you still want ??
imo

 

[Billy Bob Bob]

Thanks for the replies.

I turned the pump around as the customer said the air in the system had been happening for 2 or 3 years and then they said they had a new pump around 3 years ago. I was thinking air was being drawn down the vent and if the pump was originally the other way around then and when it was changed it was fitted the wrong way then this seemed logical, also there was red tape on the pipe so I thought it was the flow side. When I saw the pumping over I knew something was wrong, so I did some more investigation and discovered it was the return side. When I talked again with the customer I found out he put the red tape on as there was a pipe clip there and the pipe would not stay in the clip so he put red tape on hopeing it would jam in the clip better. When I siad to him that it seemed strange that this problem had only been happening for 2 or 3 years since the changing of the pump his wife said (who was not there earlier) "no it's been happening a lot longer than that"! So it was a little being misled along with my inexperiance that caused me to turn the pump around. Anyway on the up side no air was drawn in to the system during the period the pump was on the wrong way round.

Going on to some of the recommendations. I thought of an auto air vent on the rad, however it is in the main bedroom and there is so much air being drawn in to the system it could be going off when they are in bed (being a stove it takes time to cool and stop the heating process).
With the suggestion of a manual vent, would this just move the bleeding of the system from the rad to the manual vent? There is so much air (it takes about 1 minute per day to bleed the rad) then the manual vent would need bleeding every day.
I like the idea of capping off the vent, It seems logical that although there is 2 seperate circuits there is one lot of water that mixes in the boiler. The vent is basically for the water in the boiler in case it over heats so one would be sufficient.
I am fairly certain the HWC is indirect and not primatic as there is an F&E tank, if it was primatic then there would not be an F&E tank.

looking at your drawing it has to feeds and vents could you clarify why please?

 

[REDSAW]

cap the 22mm with a pushfit try that for a day or 2?

 

[Best]

My second look at the system sketch shows me the primary flow to bottom of coil & feed pipe to it & the return to top of coil with vent on it!
Maybe just a drawing error.
Def shouldn't have a vent on pumped return - or on any the pumped circuit.

 

[tamz]

I agree with Martin. The vent on the heating side should not be there. Cap it.
The vent and feed on the gravity primaries are the wrong way round. Change them.
Turn the pump to the lowest setting and balance the system. Only turn the pump as high as it needs be for the system to operate correctly which will probably be at 1.

Check the expansion for drawing air by filling a glass of water and holding it over it and turn (get some one to) the heating on. Pumps surge on initial start up. Watch the water in the glass.

If the pump is on the return leave it pumping into the boiler. It will work fine that way.
If you want to alter it put it on the flow but there is no advantage other than the system will be under positive pressure. Negative pressure microleaks always show somewhere at some time.

 

[mutley racers]

will the water get sucked up the glass if it is sucking in air? Or does it just go into the vent very slightly? Do you put the vent into the water? Or just below it?

 

[PlumbBobBob]

yes water will get sucked up if drawing air and you put the end of the vent in the water.

 

[REDSAW]

I agree with Martin. The vent on the heating side should not be there. Cap it.
The vent and feed on the gravity primaries are the wrong way round.

thought so, also strange that the system is pulling back into 22mm upstairs as there is least resistance on the 22mm vent than there is on the 15mm return from upstairs rads.
turning the pump around or reducing vent to 15mm would make a difference.
is it advisable putting on a check valve on the vent?imo.only?.

 

[MickBrown]

I went back and capped off the second vent on the central heating circuit, everything is fine now with no more air being drawn in to the system.

With regards to the primaries being the wrong way around, I double checked everything and they are definitely the wrong way round. However the customers are pensioners and have lived there since it was built at least 20 years ago, as the hot water works it is difficult to say to them they should spend money changing the pipes around. Does anybody think they should definitely be changed or leaving them as they are would be okay?