Bad air lock in cold feed

[CXR100]

had a call today, hot water dribbleing out of taps, went to address to fint once tap was left running for around 6 seconds water would slow down to nothing, so thaught it would be a blockage, so undin every joint in cold feed to find it all clear, then in the hot pipe to the first tee, all lear, so filed back up , sucked with wet & dry, still nothing, so un did cold feed at bottom of cylinde ( the gate valve was right at the bottom) and it left som air out, then water, snatched it back in and suprisingl all worked as well, so i can only turn out to be an airlock in the cold feed, anybody had this before??

 

[Best]

Cold tank must have drained for that to happen surely? Normally happens sometimes when replacing the cwt, - water stays in the cold feed level with the hot cylinder, then first air & then water above that. Just putting a cold supply (gravity or mains) through to a hot supply for a few seconds will cure it & you hear the bubbles going up into the cwt. Holding your hand over the outlet of the older mixers on a bath say & turning both taps on will sort it.
Check incase the ballvalve is blocked on cold tank.
If the cold feed to hot tank is 28mm, it will be much less likely to airlock, especially if it has a short run or is not horizontal for a fair bit in attic. 3/4" pipes were prone to airlock easier.

 

[happyflyer]

It might not be this but I have seen this loads of times.

 

[Billy Bob Bob]

had a call today, hot water dribbleing out of taps, went to address to fint once tap was left running for around 6 seconds water would slow down to nothing, so thaught it would be a blockage, so undin every joint in cold feed to find it all clear, then in the hot pipe to the first tee, all lear, so filed back up , sucked with wet & dry, still nothing, so un did cold feed at bottom of cylinde ( the gate valve was right at the bottom) and it left som air out, then water, snatched it back in and suprisingl all worked as well, so i can only turn out to be an airlock in the cold feed, anybody had this before??

get a washing machine hose connect hot to cold then fire cold water up the hot pipe end of airlock

 

[Mike Jackson]

get a washing machine hose connect hot to cold then fire cold water up the hot pipe end of airlock

Not always, sometimes it fires out of the vent. A temp cap on the vent is sometimes required, as long as you remember to remove it afterwards.

 

[Rickster123]

Not always, sometimes it fires out of the vent. A temp cap on the vent is sometimes required, as long as you remember to remove it afterwards.

Ive often wondered about this. Could you not blow the cylinder by doing that?

 

[heliotrope]

Ive often wondered about this. Could you not blow the cylinder by doing that?

No. Because the cold water feed to the cylinder is open so the water forced in through the hot water outlet,
instead of going straigt up the open vent has to go up the inlet pipe. This should blow out any air into the
storage tank.

 

[CXR100]

i tied to force it from one tap to the other many times at diferent locations, sucked & blowed with wet vac, still nothing , in the end i had to snatch the cold feed out of the gatevalve at bottom of cyliner, come to think of it, the cold feed was running a bit upwards before going down to the cylinder cupboard!!, i felt like a total idiot, 4 hours to sort an airlock 🙁, i defo thought it was a blockage tho, had laods of them lately, i dismantled all the cold feed to check! dad told me the tank must have drained in the atticc for this to happen , but she told me she had no work done to it lately and everything seemed ok till yesterday!

 

[CXR100]

is that a special pipe your using there happyflyer?? never seen a pipe start off in 10mm and increase as it goes along to 35mm 😛

 

[kirkgas]

Rather than snatch the cold feed, I would shut the cold feed valve, part drain the cylinder then turn the valve back on this usually clears it

 

[CXR100]

the gate valve was right at the bottom of the cylinder! and no drain off! and celling to close to top of cylynder to drain it all by siphoning!

 

[kirkgas]

the gate valve was right at the bottom of the cylinder! and no drain off! and celling to close to top of cylynder to drain it all by siphoning!

Are you sure there isn't a separate drain connection at the other side, what kind of idiot fits a cylinder with no drain off

 

[CXR100]

yes there was but it was right up againt the wall and i could not even connect a hose pipe to it, never mind open it! yes whoever fitted it was a complete idiot!!!

 

[Richie_77]

i tied to force it from one tap to the other many times at diferent locations, sucked & blowed with wet vac, still nothing , in the end i had to snatch the cold feed out of the gatevalve at bottom of cyliner, come to think of it, the cold feed was running a bit upwards before going down to the cylinder cupboard!!, i felt like a total idiot, 4 hours to sort an airlock 🙁, i defo thought it was a blockage tho, had laods of them lately, i dismantled all the cold feed to check! dad told me the tank must have drained in the atticc for this to happen , but she told me she had no work done to it lately and everything seemed ok till yesterday!

The ball valve wasn't partially blocked ie run a bath ball valve doesnt keep up then air gets in voila air lock?