problems with a Direct Combination unit hot water cylinder

[Paul Cockhill]

Hello i wondered if anyone had any advice as I have never worked on a combination unit before

The hot water bath tap will run at full flow for about a minute and then go down to a very reduced flow. If you turn the tap off and wait a minute and re run the bath the flow goes back to the maximum and then starts to flow slowly again.


The hot water heating system is a direct combination unit and there is no problem with the heating of the water but it seems that the hot water is empting quicker than the cold water can replace it.

It could be a problem with the pressure of the cold water as the cold water tank is filling up slowly (certainly slower than the cold water comes out of the taps) however it is flowing and not dribbling.


The cold water washbasin sink tap works well and the pressure is very good, however the flow coming out of the combination storage tank is a flow but does not seem to have much pressure and I wonder if this might mean that it cannot replace the water quick enough.

Or is this problem common with these types of combination tanks?


It also seems that the 15 mm pipe, feeding the combination cold water storage and the shower, has alot of condensation on the pipe unlike the other pipes, could there be a clue there?

any comments gratefully received

Paul

 

[diamondgas]

Sounds like you're describing something like an Elson or Rolyat type hot water storage tank. Most likely suspect, if this is the case, is a faulty ball valve supplying the hot water side as you've surmised

 

[Simon F]

It also seems that the 15 mm pipe, feeding the combination cold water storage and the shower, has alot of condensation on the pipe unlike the other pipes, could there be a clue there?
Paul

any condensation is simply due to the temperature of the pipe in contrast to the room, made more noticeable in humid air

 

[PlumbBobBob]

this time of year any mains fed cold pipe will form condensation when entering a warm atmosphere

 

[Paul Cockhill]

Thanks guys, really useful advice, might start with changing the ball valve and see how I go from there

Paul

 

[stevetheplumber]

probably only needs cleaning out