Hot water pressure low and takes ages to come through

[JP_]

I have a Baxi boiler, hot water tank in the loft of my bungalow, fed by a cold water tank in the loft. Plumber once mentioned that the pressure would be low as cold tank only slightly higher than hot water tank.

Hot water always takes ages to come through, about a minute I guess. Most pipes are in the loft, and lagged, and under loft insulation.

Even if the shower or another tap has just been used, a tap in the other bathroom is really cold to start with - not just cool, but seems as cold as the cold tap. After about a minute it warms up, but is never really hot.

Might it be that I need a new hot water tank? Or position it downstairs for better pressure? Or feed mains into it instead?

Wondering if it is just because of the low pressure that it seems worse.

Also, what would be the best way to improve the pressure?

 

[ETAF]

our setup in bungalow is similar, but our hotwater tank and cold water tank are all in one - cold on top of hot
we get enough pressure to have a shower off the bath taps OK
But it does take a while for the hot water to get to the kitchen sink, longest run about 6-8m pipe run i guess.
And we do leave running for about a minute before the hot comes through, same on the bathroom shower
Although its very hot when it gets there

After about a minute it warms up, but is never really hot.

Do you ever get HOT water , it maybe a setting on the tank thermostat, the white box lower left on picture
How hot are the pipes , cant see from the diagram
Hot water out the TOP pipe, the two sides should be from the boiler, are they hot when boiler on for hot water ?
see diagram here
https://wardgas.co.uk/hot-water-cylinders/

if you use the emersion heater to heat the water , rather than the boiler , does the water then get hot

 

[JP_]

Well, it is hot enough, and a shower can be too hot, but it is never scolding hot - not a bad thing, but in previous house it could get too hot.
Heat is not a problem, i really mentioned it just in case it was the reason for the cold taking ages to come through.

 

[ETAF]

i really mentioned it just in case it was the reason for the cold taking ages to come through.

Do you mean HOT
Just checked our kitchen, which is on mains for cold, but again travels further than hot water , and the cold and hot feel about the same temperature when first run.
just timed it
25 seconds before hot gets even slightly warm
At 15 seconds it actually felt colder
45 seconds before hot, what i would call the hotest temp
Bearing in mind ALL our pipework is in the loft, under lagging and some pipes are also lagged
BUT its very very cold in our loft at the moment, we dont have felt under some of the tiles so a bit of a draft up there
Hot water comes out of tank, travels the length of loft, then down a wall behind kitchen cupboards and along the floor around to the sink, I'm guessing 6-8 meters
The cold has to come from the bathroom main stopcock, up the wall and that is further away from the tank , so probably another additioanl 3 meters to travel

 

[JP_]

Thanks, sounds like mine is normal then. No need to spend money!
It is amazing then how much water sits in pipes, and how cold the hot water gets sitting there, even in lagging and under insulation.

 

[ETAF]

yep, i recently changed the 15mm hot water to run 22mm so we got as much flow into the bathroom shower during a recent refurb
hasn't made a lot of difference to the kitchen though as that's mainly 15mm
the 22mm out the tank, stopcock with in a few inches , then 15mm , to above bathroom, then 22 again
Also made sure we only had low pressure taps in bathroom, although we do have higher pressure taps in kitchen and that does restrict the flow slightly
At the main cock we only have 2 bar pressure
But as you know from the loft tank very little pressure.
I had to put a pressure reducing valve on cold to bath , so the shower would work well off taps.
we also have a mains pressure electric shower

Do you have 22mm for the hot throughout
you can calculate the volume of water - calculators on line,

 

[JP_]

I know there is 22mm from tank to new bathroom, not so sure about old bathroom and kitchen though.

 

[ETAF]

just checked the bath tap
22mm from tank , all the way
bearing in mind that the kitchen pipe joins this pipe just above the bathroom, so in theory , because i ran the hot in the kitchen that part of the pipe work, from tank across loft to join - is already loaded with warmer water
anyway
it took 35 seconds to get hot
25 seconds before warm
at 10 seconds water felt colder

interesting just tried the kitchen and was running warm, went cold and then at 35 seconds was hot again
so the pipes get very cold and don't seem to hold any heat in the loft, I know they are all lagged, as when the kitchen was done - they relagged every pipe in loft and so did the bathroom boys check it all, as we had new plastic pipe run for central heating so the whole area was lifted and checked

Pipe work also lagged with pipe insulation tubing stuff and is in between about 100/150mm. of loft insulation, actually probably more insulation in that area,

 

[CBW]

Your plumber is correct in stating the cold water tank in relation to the cylinder, it’s called the head of pressure. 1m head = 0.1 Bar (roughly), which judging by your photo is approx what you have. The best way to increase the pressure would be to have a pump, convert to a combi or have an unvented cylinder fitted. If you’re talking about flow rate, then that’s something a little different. How long does it take to fill the kitchen sink? Get it checked if you’re finding it difficult, it could be a blocked cold feed to the cylinder, a partial blocked hot outlet, the gate valve could be restricting the flow.

 

[bernardgreen]

Your plumber is correct in stating the cold water tank in relation to the cylinder,

Isn't the static head ( pressure at tap ) determined by the difference between the height of the surface of water in cold water tank and the height of the tap to which the water will be flowing.

Dynamic pressure at the tap ( when water is flowing ) will be reduced due to the resistance to flow along the pipe work

The hot water tank has the same effect on the pressure at the tap as a length of very large bore pipe

 

[Nige F]

Has that ladder passed a H+S check ?

 

[JP_]

I think it's probably the safest thing up there!

 

[Dangee]

Your shower could back feeding cold water into the hot water if the NRV's don't shut properly also check that it doesn't run through any section of iron pipework which will gradually reduce the bore of the pipe.