Struggling to move what i think is an airlock

[alex]

Please help me! I have what I believe to be the mother of all airlocks within the coils of an indirect cylinder on a gravity fed hot water primary although other possible suggestions would be welcomed. Starting from the beginning, the boiler (an old potterton) is located in a basement it heats two separate circuits with their own flow and returns, a pumped central heating circuit and a gravity circulated hot water circuit (22mm not 28mm) to a indirect cylinder located in the attic literally right under the Feed and expansion cistern, there are no diverter valves / external controls. Heating options should be hot water only and CH + Hot water (not CH alone). I drained the system to add a new rad + fit TRV’s to existing rads, while there i added fernox heavy duty CH cleaner to the header tank and refilled – no problems. 48 hours later re drained the system to remove cleaner and refilled with inhibitor. CH system is working flawlessly but no hot water regardless of CH on or off, when set to hot water only flow pipe heats up near boiler (but not at cylinder) and after a few minutes the boiler starts to kettle and shuts down. Went through all known methods of moving an airlock (more on that in a min) but to no avail. At this point it did occur to me maybe some of the muck loosened by the cleaner had blocked the pipe so re drained the system cut both the flow and return connected the flow to the mains and return to a drain capped off open vent and closed cold feed. Managed to push water around the circuit no problem so re connected flow + return and refilled. Assuming now that it is an airlock here is what i have tried to move it. Loosened unions on cylinder – lots of air out followed by water, still no hot water. Attached mains to open vent – bubbles out of cold feed still no hot water. Added T to flow pipe in basement and connected this to mains (like a pressurised filling loop) opened this until overflow ran don’t know if it moved any air as i couldn’t leave basement in case i over filled F + E cistern, still no hot water. Have also had a gas safe friend rule out issues with the boiler. I am well and truly stumped on this one only other thing i have ever heard of to move an airlock is boiling it out but due to distance between boiler and cylinder and age of the boiler this is not something i want to try. Ideas please could it be something else? Are there any other tricks to moving an airlock? Just to clarify i am a professional plumber so answers including call out a plumber don’t help!
Many many thanks in advance
alex

Have just read elsewhere on this forum that half a bottle of fairy liquid into the header tank then drained into the system can help to remove airlocks? opinions please? what are the long term effects on the boiler?

 

[Mbear]

Look at my thread titled 'nitemare airlock' on page 1 or 2 of the ch page. Have u tried all the things I posted on that thread?

 

[desino1]

Had similar problem
Found blockage in cylinder coil eventually!
good luck!

 

[fireblade]

Try turning the rad valves off and running the heating pump at full speed it may add a bit of flow to the primarys and shift the airlock

 

[Billy Bob Bob]

i would look at coil on cylinder,if that proves fruitless what about fully pumped conversion?

 

[alex]

Thanks Mbear i have had a look, i haven't tried closing and pressurizing the system not sure if that would be applicable without a pump but will add it to the list to try

Fire blade will also add that to my list

Gas man i had thought about a fully pumped conversion, would it just be a matter of putting a second pump on the hot water circuit? I'm not clear on how it would be wired into the programmer to function on the hot water only setting. if it helps the programmer is a Siemens one the very common design a quick Google suggests its called a RWB29

cheers for all your help guys as it happens customer is away until Monday anyway so i'v got a bit of time to devise a strategy to beat this sucker!

 

[stevetheplumber]

is the header tank full ? have you tried cracking the connection on the flow into the cylinder to release air ?

 

[justlead1]

Don,t try this at home. You have checked it open vented? turn pump off, fire boiler remove boiler stat from file when it boils switch pump on to dissipate heat and boiler of stat back in file, Now check if gravity is working. Good Luck

 

[alex]

stevetheplumber, yes F+E is full have bleed lots of air from top union of cylinder (until water flowed and bubbles stopped) still locked up.
JustLead, have heard of your technique but very unsure about putting additional stress on a very old boiler there is also a good 15m of pipework between the boiler and the cylinder where i'm assuming the airlock is so would take quite a bit of boiling.

can anyone briefly describe the alterations which would be necessary to convert it into a fully pumped system?

 

[Billy Bob Bob]

fully pumped-y-plan 1 pump for ch and dhw,three port valve,bypass,(to stop mechanical noise) cylinder stat,room stat 2 channel time clock, wiring centre try googleing y plan

 

[Blackcatgas]

fully pumped-y-plan 1 pump for ch and dhw,three port valve,bypass,(to stop mechanical noise) cylinder stat,room stat 2 channel time clock, wiring centre try googleing y plan

agree with Mark ,the way forward.

you can get smart fit y plan sytems that are all on plugs so you dont need to wire evrything into a choc box.

 

[MarkAqua]

Just wondering- did you manage to shift the airlock? If so what was it?