Low water pressure after vented boiler replacement

[intamixx]

Hello,
I have a had a gravity boiler replaced from a Potterton 80e to a more recent Valliant ecoplus boiler.
The cold water tank is in the loft space directly above the 1st floor bathroom and the hot water copper immersion tank is in the 1st floor bathroom cupboard space. A fairly normal gravity setup.
In the bathroom upstairs, before replacement of the boiler, I've always had a low flow of water into the toilet (never understood why), whilst the sink and bathtub have a good decent flow and pressure for hot and cold.
Now after the replacement boiler has been fitted, I am getting very low flow / pressure of cold water in the sink (hot is still good) and also a further diminishing flow in the toilet cistern when it's filling up. I've removed the sink taps in the bathroom and can confirm the flow is slow for the cold water supply.
Would anyone happen to know the reason for this? The cold water tank was not touched during the install, but am wondering why this is happening now.
Would a cold water pump be required now?
The ground level sink cold supply has good flow, as I believe it is being fed directly from mains.
Any help would be most appreciated.
Thanks.

 

[terryplumb]

Possible air locked cold water pipes ,how poor is the flow ?
Toilet fill valve may be a seperate issue ,partially blocked filter ,or valve itself.
Another possibility is an isolation valve on the cold feed from loft tank had been closed,and then partially opened .

 

[intamixx]

Hello,
Thanks for the response. The sink has just a trickle now compared to the free flow it had before the boiler replacement.
The isolation value from the cold water tank is a stop cock and its in the fully open position. I'm going to double check this. Given the bath tub has reasonable flow, i'm guessing it must be a blockage somewhere. Just have to find out where exactly.
thanks.

 

[terryplumb]

Does the isolation valve also close the cold supply to bath tap ?

 

[intamixx]

Yes the isolation valve feeds the bath tub, sink and toilet. There are 2 circular valves in the airing cupboard (about 30cm distance between them) I attach pictures of them. Do you know what these might be for? The upper one was very hard to turn. I haven't tried the lower one.

 

[terryplumb]

Impossible to tell what each valve isolates ,would need to follow the pipes upward. I suspect they both go to the loft tank ,one feeding the hot water cylinder ,and the other feeding cold water to some or all bathroom outlets.
You told us previously that the isolation valve from the cold water tank is a stopcock ,does that mean it's not one of the gate valves in your last pic ???

 

[Harry Bloomfield]

You need to plot out on a sheet of paper, where each pipe goes and the isolation valves on each/ where they are located. Once you know, for sure, you can attach labels firmly to the valves for future reference, plus a neater diagram of the pipework.

 

[intamixx]

Ok I have attached a diagram trace of pipes that I can see and which I think are relevant. Including that un-turnable valve (which may be the problem). I have put some wd40 on the valves as well to see if it helps. I also attach some additional pictures as well. I hope this helps. Please let me know what your thoughts are and where I should investigate some more.

 

[terryplumb]

If you close your mains cold water stop cock off ,where it enters the property , does bath COLD tap still run fully ?

 

[kidgreen61]

One of those gate valves will be stuck half open/shut they're notorious for scaling up and failing.
Plumber will have disturbed the CW one, and it's failed.

 

[intamixx]

If you close your mains cold water stop cock off ,where it enters the property , does bath COLD tap still run fully ?

Yes it still runs if I turn the stop cock off in the driveway. The cold water level in the loft storage tank goes down slightly when running cold tap in the bath tub.

 

[terryplumb]

Ok ,your pic of loft tank only shows 2 outlets ,one of which feds the hot water cylinder. If there are no other outlets ,then the bathroom cold basin tap and cistern must be fed from the same tank outlet,and as the bath runs well ,your issue must be with the branch pipe to both . Possible air lock ,restriction in the branch ,or basin tap supply ,and WC cistern both have blockages .
Is basin tap a mixer ,or two seperate taps ? As you have undone tap/s from supply pipes and told us the open ended cold supply pipe gives poor flow on the cold ,I would connect mains cold supply to it ( hose pipe to outside garden tap possibly) and blast mains water through back to tank.
That will shift any airlock.

 

[intamixx]

Hello,
Finally sorted it thanks to your help. Managed to connect a 15mm right angle tap connector into cold water pipe under bathroom sink and blast it with hose (coming in through bath window) pressure from garden tap. It removed the airlock straight away and cold flow was back to normal after that. The toilet just needed a new bottom fill valve in the cistern and now that is working too.
Thanks again.