Persistent loss of cold water in bathroom washbasin

[jonnyswamp]

As has been suggested, get your basin supplied by mains cold water
You don't want to be drinking/ingesting any of the water from the CWSC

 

[deg]

How well does the water run from the shower when on cold only?

 

[Bob2153]

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.

 

[Best]

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.)

 

[student plumber]

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.

 

[student plumber]

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.

 

[Darren Jackson]

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.

 

[Bob2153]

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

 

[jonnyswamp]

Thanks for getting back Bob

 

[RSD]

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