Cold water air lock

Thanks, flow on new sink is perfect as it's main cold and hot water gravity which wasn't affected anyway so no issues here
 
Doitproper said:
The cheaper service valves have a smaller flow diameter and may be restricting the flow more than previously. Similar if combined tails and service valves have been used. Also, ensure the tails are not kinked or twisted.
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Have you checked this?
 
Its not unusual for the flow to the sink and toilet to be affected when running the bath if served by the same pipe. Are you sure this didn’t happen before and its become apparent after doing the works.

Usually, once the bath tap is running ok (¾”) any trapped air gets sucked out of the pipes if left running for a few minutes. Once the bath is running ok ensure the upstairs toilet is full and then try the downstairs taps allowing time for any air to be sucked out. If your new sink is downstairs with the modern small connectors it is possible there may not be enough capacity to suck out any trapped air.

If systematically going through each fitting (bath/sink/toilet etc) on the pipework doesn’t work you could try disconnecting a downstairs pipe and purging water into a bucket.

Last thoughts are whether you could have inadvertently” introduced” a blockage into the system (dropped / left something in the pipe or a bit of polystyrene floating on the tank entered the pipe when it was drained) and check the new gate valve / service valve on the cwst (both for size and operation.

Without knowing the specifics of the system its difficult to troubleshoot so its a case of methodically checking the system and keeping an open mind.
 
Doitproper said:
Its not unusual for the flow to the sink and toilet to be affected when running the bath if served by the same pipe. Are you sure this didn’t happen before and its become apparent after doing the works.

Usually, once the bath tap is running ok (¾”) any trapped air gets sucked out of the pipes if left running for a few minutes. Once the bath is running ok ensure the upstairs toilet is full and then try the downstairs taps allowing time for any air to be sucked out. If your new sink is downstairs with the modern small connectors it is possible there may not be enough capacity to suck out any trapped air.

If systematically going through each fitting (bath/sink/toilet etc) on the pipework doesn’t work you could try disconnecting a downstairs pipe and purging water into a bucket.

Last thoughts are whether you could have inadvertently” introduced” a blockage into the system (dropped / left something in the pipe or a bit of polystyrene floating on the tank entered the pipe when it was drained) and check the new gate valve / service valve on the cwst (both for size and operation.

Without knowing the specifics of the system its difficult to troubleshoot so its a case of methodically checking the system and keeping an open mind.
Click to expand...
Thank you for your detailed reply and suggestions.

Cistern refill and tap use definitely worked completely normally at same time as bath cold was running prior to work. And bath cold ran with much stronger flow than now as well, so definitely a change.

The new tap on sink downstairs is mains cold so won't be affected or be contributing to air lock as far as I am aware?

"If systematically going through each fitting (bath/sink/toilet etc) on the pipework doesn’t work you could try disconnecting a downstairs pipe and purging water into a bucket" - can I just ask what you mean about this? Do you mean just try and run bath plus all the cwst fed appliances one at a time for a few mins?

If something has found it's way into a pipe to block it/reduce flow rate how can this be identified and/or rectified? Trying to blow it back into CWST via mains connected hose?
 
Yes. Give each tap supplied from the CWST a few minutes running fully open. It might suck some air out. You could also try opening them all together but not those that allow air to be sucked into the system (a long shot but nevertheless worth a go in the absence of other ideas).

Being able to disconnect a pipe from a tap and allowing it to run full bore will give it the greatest chance of shifting an airlock (but the pipe must be on the downstream end of the airlock). You are trying to minimise all resistances ie taps, isolation valves, tails etc.

If you can piece together where your pipes run you may be able to identify where any airlock may be in relation to the appliances.

Using mains water flowing back into the tank is a good idea to try and shift any potential blockage that may have entered pipes from the CWST.

I assume the tap you changed was fed from the mains previously ie you havnt changed the pipework.

Gut feeling, so long as you have tried the above, is any air blockage is likely to be near the CWST / in the loft. Do the pipes from the CWST in the loft have a continuous fall ?. Sometimes a high point can be created either under the tank or where the pipes have an elbow and change direction to go through the ceiling.
 
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