Air in system

[oscarblue]

Hi Guys, got a bad airlock problem, a few weeks back my indirect cylinder started leaking, so being a bit handy I thought I’d have a go at replacing it, all went well til it came to turning the boiler on and bleeding the system. The central heating part of the circuit is fine but as soon as you switch over to heat the hot water, loud bubbling gurgling and swishing noises can be heard from the system. I’ve tried filling the system from the bottom up, several times – no improvement. The only change to the pipework I made when installing the cylinder, was to remake the connection to the top coil tapping as the new connection was about three inches higher than the one on the old cylinder, so thinking that might be causing the problem I have since remade that connection taking the pipework above the level of the tapping and installing an automatic air vent valve at the highest point, but its no better, when filling the system there was a small phut from the valve but nothing since and the system is still gurgling etc, any ideas?

 

[newbie1]

have you gone into loft and checked the angle of the pipes in loft as air is a bit sneaky and can sit in very awkward spaces
assuming tank in loft has cold water in then next step is poss blockage of air/sediment in pipework
if all else fails you could try a reverse fill using mains(2 man job)

 

[oscarblue]

Thanks for your reply Newbie, if by reverse filling you mean filling the system from the lowest point, I have done that several times, both from the lowest drain cock( radiator in kitchen) and from drain cock just above the boiler, to no avail. The system fills the header tank via both the supply pipe and the vent pipe, so no blockages there, it seems to me that the air must be trapped in the part of the system between the diverter valve, cylinder coil and pump as the system is perfectly silent when the diverter valve is switched to central heating, I'm just at a loss to know how to purge it, maybe ear plugs are the answer, lol.

 

[Bernie2]

I would suggest running the cylinder flow level with only a slight rise to a tee piece air bleed on the level run.
Sometimes, when you fill a system, the water rises up the return as well as the flow at the same time and traps air in the cylinder coils. The thing is, to vent the air at the moment its got to fight against the rise in the flow pipework to reach the tee and air bleed leg.

 

[oscarblue]

Thanks Bernie, yes i see what you mean, but when the system is not operating would'nt you think any air trapped in the coil would find its way to the bleed valve?

 

[newbie1]

is the water coming out of the hot taps when you open them??only other thing i can think of is maybe introduce a water pump driven by a drill then open up lowest drain point and force water round the system and hopefuuly dislodge the air
assume 3 port valve is moving freely

 

[Bernie2]

Yes you would think so, but I have had plenty, that haven't it depends on a few things such as frictional heads. The cylinders internal coils may be over a a couple of meters long in a normal cylinder. So in reality the water rising up the flow may beat it to the top of the cylinder coil and start to flow down toward the water rising in the return.

I know water is supposed to find its own level but its working against frictional heads here, so unless you where to fill it very very slowly allowing time for both heads of water to equalise you will probably trap air.

I once worked on a job where every circulatory flow primary was required to be set with a level whose bubble was just off centre or they wouldn't work. I had the job of going back to make sure that most of the ones that didn't work where put right.
What a pain.

Saying that of course I have seen many cylinder Primary flows put in like the one you show as well. Being honest, I have forgotten why they do it like that. I am sure somebody else may be able to help on that one.

 

[Plucky]

Is your auto air vent defo working. Crack the compression nut and see if you have water/air or nothing there. Old towel underneath for safety!!

You could try switching system to HW only and flicking the pump on and off. Sometimes this 'pulsing' effect helps to shift stubborn air locks. In between pump speeds 2 and 3 the pump will shut off so you can turn pump on and off this way.

newbie what on earth has running the hot tap got to do with it. And attatching a drill pump to the lowest point?!?! interesting

 

[oscarblue]

ok Bernie thanks for your help, I was kinda hoping there would be something obvious that I had missed, but I think I'll leave it a few days and see what happens, I only fitted the vent yesterday so maybe the air will work its way out in the fullness of time, ear plugs in the mean time

Thanks plucky I will check air vent, system is hot at the moment so maybe later, will also try your pulsing, but I think Bernie is right, when pump is operating its trying to force the trapped air away from the vent and I think that may be my problem

 

[newbie1]

Is your auto air vent defo working. Crack the compression nut and see if you have water/air or nothing there. Old towel underneath for safety!!

You could try switching system to HW only and flicking the pump on and off. Sometimes this 'pulsing' effect helps to shift stubborn air locks. In between pump speeds 2 and 3 the pump will shut off so you can turn pump on and off this way.

newbie what on earth has running the hot tap got to do with it. And attatching a drill pump to the lowest point?!?! interesting

was just trying to ascertain that the cold feed to the tank had filled it and there wasnt a possibility of the noise being air inside the tank but thks anyway
and what i said was not attatch to lowest point but open at lowest point and use the pump to force water through the system to force the air out rather than relying on gravity and air rising

other option is attach main to drain off close rad valves so water is just going round the pipe circuit have someone in loft in case of flood and try to force the air out similar to using a drill operated pump otherwise you are relying on gravity to shift the air just trying to give you a few options in case anyone else wants to pick holes

 

[JSPM]

I am new to this plumbing lark but had a similar problem with a trickle from a monobloc tap after a system draindown and refit of the monoblock tap. (Drained down due to poor shut off valves). So to clear the air from the system I fully opened the hot tap that had the poor flow, put the palm of my hand over the spout of the tap to create a seal then turned on the cold tap. This forced the cold back through the the hot tap pipework and "gurgled" out the air lock. Hope that helps.
Dave.

 

[heinz57]

Could you not try using a waterhoover to suck out any trapped air?

 

[Hugh]

buddy close all rads apart from one, take the bleed screw out of the central heating pump and wait till all 4 corners of the radiator heat up then close that radiator and move on to the next one works a dream for me ever time

 

[stevetheplumber]

Hi Guys, got a bad airlock problem, a few weeks back my indirect cylinder started leaking, so being a bit handy I thought I’d have a go at replacing it, all went well til it came to turning the boiler on and bleeding the system. The central heating part of the circuit is fine but as soon as you switch over to heat the hot water, loud bubbling gurgling and swishing noises can be heard from the system. I’ve tried filling the system from the bottom up, several times – no improvement. The only change to the pipework I made when installing the cylinder, was to remake the connection to the top coil tapping as the new connection was about three inches higher than the one on the old cylinder, so thinking that might be causing the problem I have since remade that connection taking the pipework above the level of the tapping and installing an automatic air vent valve at the highest point, but its no better, when filling the system there was a small phut from the valve but nothing since and the system is still gurgling etc, any ideas?

just looked at the picture does the flow and return from boiler go up and over in the loft and feed down to cylinder? if so there could be air vents on pipework in loft