Low Mains Pressure

[cocoots100]

I recently replaced the ball cock in the water tank in the loft. As the internal stopcock under the stairs was so stiff it could not be turned, the water supply was shut off from the mains stopcock outside the property. When the water supply was turned on again, the water pressure in the kitchen taps and the pressure going into the loft tank was considerably less than before. Both of these are fed directly from the mains. The mains stopcock has been opened fully. Tres bizarre.

 

[Bahco]

Check you have opened the outside stoptap fully.
Better still turn off again and replace your internal as you may need it one day

 

[ChrisR]

Possible you closed the internal stopcock a bit?
Try loosening its spindle seal - the nut under the T handle which goes around the spindle. Then warm it up with say a heat gun (with water not flowing!) Then holding the body of the tap you can usually get them moving a bit. You can use a spanner on the head but not too strongly or you'll just break it all.

 

[kevplumb]

washer come off and restricting flow

 

[cocoots100]

The internal stop cock has always been jammed in the full open position, which is why it is probably jammed in the first place.
The only thing which had changed was the installation of the ballcock in the loft tank and the turning of the outside stop cock.
How would I check where the washer has come off and restricted the flow?

 

[croydoncorgi]

Is the pressure 'normal' (as before) with the kitchen tap running VERY SLOWLY? Then, does the pressure DROP when the tap is turned on more? If so, chances are that there is an obstruction in a valve somewhere. Since only the street valve was turned off, it's probably in there. Dislodged washer is favourite. Your only practical option is to call out the water company and hope they do not ask too many questions about why you turned it off!
As has already been suggested, fix your internal SV first!

If , on the other hand, the pressure is low whatever the flow rate, then the mains pressure really has dropped!

There are those (probably not here!) who believe that partially turning off a stopvalve will reduce water pressure - yes, it will, but ONLY when the flow rate is high enough that the constriction causes a pressure drop. At low flow, there will be full pressure on both sides of the valve.

 

[cocoots100]

Thanks croydoncorgi. Yes, the pressure does reduce after the tap is turned on. However, it reduces from a very low pressure to an even less pressure. Takes about 15 seconds to fill a pint glass.
They say some things are worth waiting for, but a pint of water is not one of them.
Looks like a call to the waterboard is on the cards.
Many thanks to all who have replied.