Dunsley Yorkshire air sucked in

[Tomugli]

Hi great forum We have read many times for help along the process of renovating our home.

We are hoping someone can offer us some advice on our plumbing problem. we have a Yorkshire boiler stove. It is on the ground floor at the back of the house and is fed from and f/e tank in the loft (5.3m ish up). two 28mm pipes run up to the cylinder and are t'd off at 22 to run through the ceiling cavity to a heat loss rad. the 22mm Central heating pipes (the stove has 4 rear ports) run up to the first floor and feed 2 rads, then the pipe slims down to 15mm (re used circuit from the old back boiler) and feeds one more rad upstairs finally dropping into the front room to the final rad on the circuit. The pump is in the flow. When we run the pump with the system cold it runs absolutely fine, but when it is running hot, air gets sucked in from somewhere and fills up the first two rads in the system. Primaries seem to keep working fine, heat loss rad is hot etc. this only seems to happen when the central heating is pumping hot water. Any ideas how we can stop this happening?

many thanks for any help you can offer.

Tom and Laura

 

[Best]

Hello and welcome. Is there an auto vent fitted high up on any pipe on radiator circuit?
Or is there water pumping up the gravity vent into expansion tank?

 

[Tomugli]

Thanks for the quick reply!
No aav fitted on the rad circuit Currently, reckon that might be the way to go? I was wondering about extending the flow pipe that goes up from the pump where it elbows into the floor/celing cavity with a T and popping an auto vent on the top as a solution?
Water is not pumped up the gravity side of the system as this is on two separate ports on the rear of the stove. There are four ports, two feed the pumped c/h and two the gravity.

Cheers, Tom

 

[Best]

Tom,
Auto vents are better avoided. You really don't need them on a gravity filled open system usually. They tend to leak badly and can actually absorb air.
There is something strange that you are getting air filling first couple of rads. Air in an open vent system is absorbed when system cold & released when system heats. Normally this air is only small volume & will not hugely fill any rad instantly, but instead take weeks or months at worst case.
I think you have air absorbed from the pump/boiler area, assuming your pipe description is complete and correct.
Needs the pump and its pipe checked for cracks, leaks at valve connections etc

 

[Tomugli]

Do you think perhaps air could be being sucked down the vent pipe? I can try lifting the tank at the weekend see if this helps. I have heard a glug as if there's a bubble being sucked through the stove on occasion. so far I've tried pump in the flow and return, slower pump speed which is better and 2 different pumps.

 

[Best]

Don't alter the height of your f&e tank! As long as it is above the height of the highest point of the heating system parts and flowing pipes by one or two metres, it will work usually okay. The vent pipe is better well above the height of the water in f&e tank though. No harm in the vent being risen at LEAST a metre up before dropping down into the f&e tank.
To rise the f&e tank means you end up rising the vent pipe, - so no advantage except you are giving system slight more head of water, which is pointless if head is adequate at present.

 

[Best]

You could try filling a clear tumbler with water and holding the end of vent into the water while the pump is running & system hot if you are trying to prove if vent sucking.

 

[Tomugli]

Ok cheers. I'm clutching at straws! I can't figure out why it only happens when the system is hot.

 

[Best]

Ok cheers. I'm clutching at straws! I can't figure out why it only happens when the system is hot.

That's why I am thinking perhaps a crack somewhere.
It is also possible for a pump on your rad circuit to be pumping up the gravity vent when system running & especially when hot. What can happen is the pumped flow will go around the rads and back through their returns, then into boiler return connection and partly go up the vent.
So what I am saying is, if you haven't already checked for this, then do so before you go any further.
You also must have solid fuel fires & stoves controlled by a thermostat (usually best a pipe stat on return pipe at cylinder) to control the pump on & off as heat rises & falls, to prevent fire boiling up etc. That would also cause air.

 

[Tomugli]

Thanks for all your advice, I really appreciate it.
There are pipe stats controlling the pump as you described. How would I go about checking if the pump is flowing up the gravity vent and rectify this if it is?

 

[rickgumm]

is there a safety valve on the system as i have known them to pull air into the system when hot and the pump is running as the spring inside can become weak when hot??

 

[Best]

Rickgumms ^^ excellent point about a safety valve is one I never thought of!

As to how to check if pumping up vent, - best to visually look in f&e tank.
The pump correct direction needs checked also.

 

[Tomugli]

Cheers will try the tumbler tonight.
There is an aav on the heat loss rad.

 

[Tomugli]

Pump is in the correct direction definitely.

 

[Tomugli]

Good evening. We did the cup of water vent pipe test this evening and found that when the pump kicks in, it sucks the water up, spits it back in and bubbles a little. I'm guessing this means it is sucking air down the vent and that I need to do something with the pipe work to the tank. There is a horizontal ish (still downhill) run of about 3 feet of pipe from the tank to where the feed pipe goes vertical. Is it worth relocating the tank to make this run more vertical?

Thanks again for the help and advice.

 

[Best]

It is normal that the vent will suck as the pump starts. That might be perfectly ok

 

[Tomugli]

Ok that's something then. So I'm looking for a crack or leak. Am I right in assuming that if the actual boiler is cracked I should expect air from the vent when the pump is not running. This seems unlikely I've inspected visually/felt it up and there's no leaks or anything. A dose of fernox leak sealer perhaps? I shall be calling a plumber tomorrow to come have a look anyway. Will keep you posted.

 

[Tomugli]

Have been examining the system thoroughly all week (the bits I can get to anyway) and I've found what appears to be a small (1/4" across) crack on the second rad in the system. It's about 2" down from the top. It's not leaking when cold but am I Correct in thinking this could be drawing in air when the system is warm and running? This is the rad that seems to collect the most air.

Cheers

 

[Tomugli]

Hi again.

after replacing a section of pipe work under the floorboards with a small leak the problem has moved.... The pump now sounds like it is pumping air through it. This only happens when the system is hot and gets worse the longer it is running. After the pump there is a magnaclean which I can now bleed the air out from when it's been running for a while. I've had a plumber/heating engineer friend round who can't see anything wrong with the system, he did say these systems are always a pain though. He advised me to extend the vent pipe, which I have done to no avail. There is now no or at most very little air in any of the upstairs rads.

Please any ideas,

Cheers, Tom

 

[Norcs]

Hi again.

after replacing a section of pipe work under the floorboards with a small leak the problem has moved.... The pump now sounds like it is pumping air through it. This only happens when the system is hot and gets worse the longer it is running. After the pump there is a magnaclean which I can now bleed the air out from when it's been running for a while. I've had a plumber/heating engineer friend round who can't see anything wrong with the system, he did say these systems are always a pain though. He advised me to extend the vent pipe, which I have done to no avail. There is now no or at most very little air in any of the upstairs rads.

Please any ideas,

Cheers, Tom

I had this problem with my stove for a few years. The pump gushing with air and filling up the rads with air.
Constant bleeding every few days.

At first I thought the f&e was too low so raised it as high into the apex of the roof as possible. Lived with for another year.

Then this year I removed the 15mm T just before the pump (which split the primary return from the two rads) and fitted a 22mm T.
Now no problems.
Just too much restriction on the pump inlet and it probably sucked air in through the pump isolater gland seals or flange seals or possibly the compression T seals.

 

[Tomugli]

Thanks for the advice. It has been better since I switched out the old 15mm section of the rad circuit that had been 're used for new 22mm (feeds the last 2 rads) as you say. I think now it must be one of the pump seals as that's the only place it can be coming in. The rad circuit is separate to the f and e cos it's a 4 port stove. I only seem to get the air now when the system Is hot enough for the return to be hot at the pump.

Cheers