View the thread, titled "Hot water cylinder, poor flow and cold water to kitchen." which is posted in Plumbing Advice for Any Other Country on UK Plumbers Forums.

C

Corkplumber

I got asked recently to have a look at someones hot tap in their kitchen. It's an ordinary semi-detached two floor house . The tap is downstairs and fed by an indirect copper cylinder on the next floor with a vent going to the cistern in the attic. This was apparently always the setup.

The residents say it takes minutes at a time for hot water to come through and that the rate of flow isn't adequate. They say it has been like this since a plumber replaced an old cylinder for the current one. Looking into the hot press I can't see what is wrong, you have the hot draw off coming directly off the top of the cylinder and seems to continue for the standard length before the tee for the vent and fixtures.

One thing I did notice is that the horizontal draw off pipe on the top of the cylinder has a very noticeable slant. Could that have an effect on the rate of flow in the kitchen?
One of the residents says that when the hot draw off reaches the tee for the vent and fixtures, where the pipe continues downward and under the floor that it is reduced to 1/2" or 15mm quite soon. He says he witnessed this when last the hot press was being worked on. Could this cause a problem?

The bathroom upstairs has no reported problems with flow rate or the amount of time it takes the hot water to come through. Maybe boiler and immersion settings should be looked at? I don't think a secondary return is the solution as this problem is only recently occurring and the house is an ordinary residential house.
 
First of all, check the tap in the kitchen isn't blocked slightly with a bit of scale etc from the old work when plumber disturbed it. The tap, if it is a mono bloc it will be easy for dirt to have slowed the flow & the diffuser at the end of the tap neck may be blocked. A bit of foam of the new cylinder can cause this too.
 
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Draw off should have no effect on flow even if it is dropping a little to the vent. The 15 mm pipe is fine for the hot to downstairs & will only cause problems if other supplies are off it & any are turned on at same time as kitchen.
 
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