Intermittent hot water

[andym01480]

I have an indirect heated hot water tank fed from loft tank. Cold water pressure from tank is consistently fine.

The hot spurts and often has low pressure (20 mins bath fill not 5mins). Water hot - 65oC ish. This happens particulary on first use in morning 1hr after system comes on, at lunchtime and after work, when it has been standing a few hours.

The only change we have done recently is reinstalling kitchen sink - when I turned off hot stop cock feeding to hot tap under sink while doing it and then turned it back on. No leaks.

Any ideas?

 

[Slugbabydotcom]

There is either a blockage on the supply pipe from the tank to the cylinder or on that pipe the gate valve has been left partially closed.

 

[steved101]

is the cold water tanks lid off? does it look clear inside?

 

[andym01480]

Cold tank, lidded andinsulated, very clean inside!
Gate valve from cold water tank to hot tank broken - doesn't move and not been touched!
Stop cock on hot feed to kitch sink is on.

The intermittent spurting and low pressure on all hot taps, upstairs and downstairs. Hot tank 20 years old btw, very high limescale area - toilets need descaling every fortnight....

 

[poolebybirth]

probably a build up of limescale, usually in the pipe that leaves the how water cylinder then - may have noticed a gradual in flow overtime from your hot water taps.

 

[andym01480]

So how do I fix that?

 

[poolebybirth]

need to close off cold feed to the cylinder, open hot taps fully, unscrew connection at the top of the cylinder, but may be v stiff so be careful, have a bucket ready also, then you will probably see the scale build up, which you will have to remove, or if too bad, cut out the section required and re-pipe.

 

[andym01480]

Are you saying the scale build up is just likely to be "catching" as it turns the corner coming out of the top of the pipe - or could this be furring of every pipe in the house?!!!

Someone (off forum) also said that the tank could be filling with scale like a kettle and is "kettling" - but I have only seen the word kettling associated with boilers on this forum. Is that a possibility and is there a way to diagnose?

 

[poolebybirth]

if the coil in the cylinder was scaled up then you would get hot water at normal pressures as before, just it would take longer to heat up and you may get a lower temp.

it is usual for the pipe leaving the top o the hot water cylinder to get scaled up, especially in hard water areas, over time. thus reducing your hot water flow from all taps.

 

[andym01480]

Thanks. Will do it on my day off tomorrow! At least it is not a whole hot tank or all the pipes.