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Hi All,
Would appreciate some advice. I have just had my cold water storage tank in the loft replaced and after 2 to 3 days I lose all pressure in the cold water supply to the mixer tap in the wash-hand basin. The plumber who did the job said it was an airlock and back-flushed the open cold connection using the supply from our power shower. After a day the flow began to diminish again and on day 3 it became a trickle only. Plumber returned and back-flushed again and the flow was reinstated but the same has happened again after 2 to 3 days but this time the is no cold water at all. He has recommended that we have additional work done by tapping into the cold water feed to supply the washbasin and toilet. All other cold water taps in the house are working OK and the problem is limited to the cold water supply to this one mixer tap. This is the first time I have had this problem and the back-flushing seems to only be a temporary solution as the pressure drops of over the next couple of days. The plumber says it is not related to anything he has done? Any suggestions as to what may be causing the problem and is his recommendation of connecting direct to the cold water feed the right thing to do? Appreciate any feedback.
 
The plumber who did the job said it was an airlock.

Unlikely unless the pipe that feeds the problematic tap rises above the level that it leaves the tank at. This shouldn't be the case if the new tank was installed properly.

If that's not the problem, you've either got a faulty mixer tap or (less likely) a foreign object somewhere the pipe that is moving into a position where it's blocking the flow or interfering with the tap opening. Does the mixer tap valve feel 'normal' when you operate it?

A few photos of your pipework and new tank would be helpful.
 
Unlikely unless the pipe that feeds the problematic tap rises above the level that it leaves the tank at. This shouldn't be the case if the new tank was installed properly.

If that's not the problem, you've either got a faulty mixer tap or (less likely) a foreign object somewhere the pipe that is moving into a position where it's blocking the flow or interfering with the tap opening. Does the mixer tap valve feel 'normal' when you operate it?

A few photos of your pipework and new tank would be helpful.
 
The mixer tap feels normal. After it has been back flushed it flows good but starts to decline over time (2 to 3 days) until it becomes a trickle or stops altogether? Unfortunately the loft access has been resealed so it is not possible to get easy access to take some pictures. Could do that once the plumber returns. I just find it strange that the flow diminishes over time that would imply a gradual ingress of air if an airlock is causing the problem and back flushing does not cure the issue permanently. Has me baffled as to what could be the possible cause, especially with the loss being gradual and being limited to the one tap, everything was OK until the tank was fitted and the main supply turned on. It sounds from the other post that having the supply direct from the main supply would be advisable for health reasons? Was just trying to avoid the additional expense for the extra work if the root cause could be readily identified and fixed without the extra re-plumbing.
 
The mixer tap feels normal. After it has been back flushed it flows good but starts to decline over time (2 to 3 days) until it becomes a trickle or stops altogether? Unfortunately the loft access has been resealed so it is not possible to get easy access to take some pictures. Could do that once the plumber returns. I just find it strange that the flow diminishes over time that would imply a gradual ingress of air if an airlock is causing the problem and back flushing does not cure the issue permanently. Has me baffled as to what could be the possible cause, especially with the loss being gradual and being limited to the one tap, everything was OK until the tank was fitted and the main supply turned on. It sounds from the other post that having the supply direct from the main supply would be advisable for health reasons? Was just trying to avoid the additional expense for the extra work if the root cause could be readily identified and fixed without the extra re-plumbing.
 
Repipe the mains to the cold tank supply in the roofs pace. Job done ;)
If I've understood correctly, to connect the mains directly to the tank supply line, does that mean I didn't need a replacement tank in the first place? My understanding was the tank is needed because it gravity feeds the hot water tank? Apologies for my ignorance.
 
Yep you would need to keep the tank to feed your hot water cylinder. Changing your cold water to mains would save a lot of flapping about. As long as you don't have a mixer shower as this would give you different pressures and this would not be good.
 
Yep you would need to keep the tank to feed your hot water cylinder. Changing your cold water to mains would save a lot of flapping about. As long as you don't have a mixer shower as this would give you different pressures and this would not be good.
We do have a mixer shower that is supplied from a branch from the tank supply line? The plumber recommendation was to take two separate branches from the main supply line and connect to both the washbasin cold feed and the WC cistern feed. Would this be the best way to go? The existing feed to the Washbasin and the WC are branches of the main existing cold supply from the tank.
 
How well does the water run from the shower when on cold only?
It runs OK as it is fed from a pump unit in the loft to which both the cold and hot supply are connected. I guess the pump unit has a regulator to control the mixture to the showerhead. What has recently happened now (10.30pm) is the toilet cistern is now also not filling with water - that never happened before even with having the sink tap problem.
 
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Could be blockage inside the cold pipe. That will need checked first and best way would be to have the float valve on toilet cistern diconnected or taken apart and pipe and valve flushed.
A bit of fibreglass loft insulation, or piece of hairfelt lagging for example, will block the pipe easily and back filling will maybe only temporary unblock the tap. Highly likely.
Another possibility is air drawn into the pipe, but that is easily proved when back flushing because air would be seen and heard coming into cold storage tank in loft.
(I suspect on one job I have been trying to sort, where the gravity cold to bath and toilet has air locked suddenly on several occasions, - I think it was the cold bath tap washer, but that's a rare one.)
 
It's not only dirt that can get into the cistern from the loft.
Limescale build up can trap or restrict some water in the bottom of the cistern and it won't circulate properly, and then it can turn horrible.

At the same time as trying to clean it out, you stir it up, and you really wouldn't want to put a toothbrush in that.
 
Although there are two recognised systems, direct feed (mains fed) and indirect feed (tank fed).

You can take connections from the cold cistern for a bath or shower, (which is perfectly normal), so the pressures wouldn't be so great on a mixer.

But considering what the tank water can look like, you might want to exercise caution with regards to brushing your teeth in that cold water; even though washing in it mixed with hot water isn't given a second thought.
 
Am I correct in saying that the feed to the toilet and sink are branched off the same supply to your thermostatic shower pump? If so when the shower pump is running it could be pulling water from the pipes feeding the sink & wc and getting air locked. You then back fill and all ok again until the shower eventually sucks out the water again and the cycle repeats. The feed for the sink and wc should be separated from the shower feed by Tapping a separate tank connector into the side wall of the header tank independent to the shower feed.
 
Am I correct in saying that the feed to the toilet and sink are branched off the same supply to your thermostatic shower pump? If so when the shower pump is running it could be pulling water from the pipes feeding the sink & wc and getting air locked. You then back fill and all ok again until the shower eventually sucks out the water again and the cycle repeats. The feed for the sink and wc should be separated from the shower feed by Tapping a separate tank connector into the side wall of the header tank independent to the shower feed.
Hi All.,
Have been away on business the last couple of days but as an update I would like to thank everyone that contributed for their very useful and expert advice. As a result of the majority of feedback I have had the offending wash basin and toilet connected directly to the main supply to bypass the cold water storage tank. For interest this revealed an additional problem in that the washbasin mixer tap was leaking at the mixer handle due to the pressure being too high and exposing a failure between the seal and the lever that was not evident when on the lower pressure. As suggested by "Best", in combination with the power shower being on the same cold water supply, this may have well have been the source of my problem. After replacing the mixer tap with a new one everything is working OK with no further apparent problems.

Once again I would like to thank everyone that responded for taking the time to provide such valuable advice in deciding the correct way forward to fix the problem.

Kindest Regards
Bob
 
Who supplied the taps - could they have been for 'high pressure' only?
 
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