Trickle from bathroom sink cold tap need help please

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Hi,

I am a keen DIYer so please be kind. I have done my best.

Have an issue with what I think is airlock and need some help please.

My system in my modern 2012 home comprises a megaflo cylinder for mains pressure hot water, condensing boiler and no loft tanks.

Earlier in the week I replaced the kitchen mixer tap as the old one was leaking from the body. As usual cut off the water at mains cold and at the hot tank. But also drained the tank and reset the air gap as I have a few times in the past. Swapped the tap no worries and all is well there.

Ran all the taps one by one, let them do their spitting carry on. All well.

Day later realised the bath upstairs was running slow on the cold side. We've had issues with the tap valves, so turned off the mains cold again and swapped out the valve. Things seemed much improved.

Today notice the sink and toilet are slow in the same bathroom. Presume airlock, but as I had some spare tap valves, replaced that using isolator on line under the basin. No improvement in flow.

Bath excellent in that room, as is shower. All hots ok. Just sink cold and toilet which is next to it slow.

Figured air lock, so tried the hose on to another tap trick a few times. Nothing, well other than me getting a bit soaked. Still trickling.

Took toilet's siamp style fill valve apart in toilet to check it. Removed the diaphragm and ran the water. Flow there was tiny with tap on, little more of a flow with it off. Rubber diaphragm ok. Toilet does still fill though, albeit quite slowly. Put it back together.

Also tried attaching the water hose from a working tap to the open toilet valve and blowing it back to attempt clear airlock. No change.

Tried turning cold water off again. Opening all taps a bit. Water back on. Open the taps wide in sequence up to the trouble one. No change.

I don't want to apply too much more reverse pressure, as the house has a pipe organ of plastic push fits in the void which I would have a mare on my hands if one blew off. Mind you I did get brave and go for it a bit with the hose trick. Still nowt.

What might be going on and do I have a hope of solving it. Considered and more experienced help very much welcomed.

Thank you
 
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durhamplumber

Today notice the sink and toilet are slow in the same bathroom. Presume airlock
Unless I am being completely thick,an airlock would never affect the cold water mains supply to your toilet.You sure the stoptap is open?
 
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hi,

All stops and valves very much open.

Taps and showers elsewhere all work fine. Just thus sink and seemingly it’s associated toilet affected by very low flow.

I’m assuming air is the culprit as I’ve drained the system recently and I’ve tried replacing the tap valve and disassembled the toilet valve with no change.

There was the usual small amount of air spit when I finished work and put things back on. All other taps thunder out, hot especially good since tank air gap reset. Just this tap and toilet that are playing me up.
 
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It's all mains pressure...you don't really get airlocks.
Open the isolating valves to the basin/WC and check the flowrate there...work your way upstream.
 
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Meant to add, I took tap internal valve out completely and opened the isolator. Risky I know but was desperate. Still only trickled out.
 
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It's all mains pressure...you don't really get airlocks.
Open the isolating valves to the basin/WC and check the flowrate there...work your way upstream.

The bath and shower next in line work perfectly, so not sure what more I can check?
 
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With both service/isolator valves open for basin and toilet, the basin cold trickles as does the toilet. Toilet speeds up a bit with basin tap or isolator off. Tried various combos with bath also on/off and no change.
 
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Having read a few other threads, my next attempt has been attaching a wet vac to the offending tap. It pulled a tank full on the vac, but no change to the flow on the tap.
 
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Nah...wasting your time with a wet vac..mains pressure will blast the air out.
Are there check valves under the basin...I've had them fail before.
 
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There are. However that wasn’t touched when I did the other work and this tap failed without them being messed with. I used the isolator under basin today to strip tap and replace inner valve. Also then to run it with no valve. Still the flow was minimal. Turning the isolator on and off seems to make no difference to the flow, but it works cutting it to zero.
 
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You need to disconnect the pipe from the outlet of the isolating valve and check the flow at that point...
 
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Ok that’ll be tomorrow’s job then. Will be scary for me as I’ll be taking it off at the copper pipe as it comes out of the wall. There’s an integrated flexi with isolator from that to the problem tap. Seems odd to me that the toilet is also slow.
 
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Whilst investigating this evening. The toilet hisses and gargles a bit when I turn the tap in the basin on/off. Is this of significance?

One vid on YouTube showed an in-line filter at the base of the toilet filling valve. Is there a chance this is blocked and causing the issues?
 
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Ok so lots of further investigation today.

Removed the toilet supply flexihose and separate isolator valve to the toilet and checked for blockages. Also pulled the in the line filter to check for debris. Nothing much to speak of there. Ran the flexi in to a bowl and water running freely. Reconnected and moved to the sink with the problem cold tap.

Removed the tap supply flexihose with built in isolator. Checked it was free and no blockages or a broken valve. All seemingly well. Ran pipe in to a bowl and reasonable flow. Added tap to the loose pipe and strangely flow from the tap had improved over previous trickle.

Decided to then replace the tap flexihose with built in isolator for a new one, just to be sure of no problems there.

Once all back together and water back on, the flow at the tap has certainly improved, yet is still weaker than other taps in our other bathroom and bath etc. At least it is now usable.

Something very odd going on.
 
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You probably had/ still have some debris in there , pressed hard against the isolator valves by the mains pressure. A lot of isolator valves have very narrow holes in the "ball" that rotates. Maybe the debris was dislodged during all you other work and found its way there.
 

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