How long does it take your water tank to heat up?

[Anticyclone]

I just had a bath with probably used up most of the hot water in the tank. Now an hour and a half after I filled the bath, someone else wants one, and there is not enough hot water to fill more than a copy of inches of the tub. Is this normal? How long should it take to reheat an entire cylinder of water? The hot water has been on permanently since 9am because I predicted this problem!

Sorry that should say hot water been on since 8am.

Arrg! "a COUPLE of inches"

What colour is the cylinder?

How hot are the radiators - i.e. how long can you hold the tops for?

p.s.

You do mean it is heated by your gas boiler? Not an electric immersion heater?

Do you live in a hard water area? How old is the hot water tank?

Apologies for slow reply. It's a yellow cylinder, yellow foamy outside anyway. The radiators are pretty hot! Yes it's being heated by our gas boiler. Yes we live in a hard water area. No idea how old the tank is.

We changed our yellow foamy cylinder (hard water area) for a new cylinder a couple of years ago and it refills and reheats so quickly we can have back to back baths now. Amazing!

Yellow is rather old, I think about 25-30 years, and does not heat as fast as a modern one (it has a smaller heat exchanger coil inside).

If the boiler is also quite old, it may be less powerful than a modern one, and so if the radiators are all on at the same time, they may be drawing more of the heat that the boiler generates.

Experimentally, turn the room thermostat down until it clicks, and the cylinder should heat more quickly.

Very old systems may have an unpumped HW circuit, and be very slow to heat the cylinder.

If you can photograph the pipes coming out of the boiler, and those around the cylinder, we may be able to identify the layout.

Look for the pump
www.screwfix.com/p/grundfos-ups2-15-50-60-central-heating-pump/42635#_=p

and a motorised valve
www.screwfix.com/search?search=port+valve

and show us the pipe layout round them

The cylinder may have a thermostat strapped to it, about a third up from the bottom.
www.screwfix.com/p/honeywell-l641a-cylinder-stat/40051

Or not.

Your hot water cylinder is most probably filled with lime scale. This forms on the walls of the hot water cylinder on the inside. At it gets hot/cold the cylinder flexes and the lime scale falls off the walls into the bottom of the hot water cylinder. This process repeats every time it's heated up. So over the years the coil, which heats the hot water via your gas boiler, gets covered in lime scale and reduces the efficiency/ increase the heat up time of the hot water. You need a new hot water cylinder.

Thanks for the replies. It is a modern boiler with a pump, and a motorised valve and thermostat on the cylinder. It does sound like the age of the cylinder and limescale might well be the main causes of the slow heating. Is it standard the heating systems prioritise hot water over the CH? Or do they try and do both at the same time?

does the motorised valve have three pipes going into it, in a T shape?

One of them will go to the cylinder, and one to the radiators.

It is possible that the radiators are taking too much of the heat, and not enough to the cylinders. This can be adjusted.

Please try it with the radiators turned off, and tell us

• how long does the cylinder now take to heat?
• are any of the radiators still getting hot?

How are you getting on with those photos?

Thanks Piglet John. Apologies for the time this is taking, will do photos soon, just dealing with a 3 week old and a toddler at the moment!

Cylinder photo

It looks to me like your motorised valve has only two pipes going into it (an in and an out). The pipe looks like it might be 28mm diameter rather than 22mm.

So unless you have another 2-port valve controlled by the room stat, to turn off the radiators, I think you may have a gravity (convection) feed to the cylinder. This is always slower because the heat from the boiler travels more slowly. It may be worse while the radiators are being heated.

If you can photograph the pipes round the boiler and the pump it may become clearer. Also, feel the two big pipes going into the LH side of the cylinder. One should be "too hot to hold" and the other should be "too hot to hold for long"

This is quite an old design, but the system can be modified without much difficulty.

The valve with the round red head is used to restrict flow to the cylinder so it doesn't take all the heat, leaving the radiators cold. It can be adjusted a bit, but don't do that unless you have a plumber in the house, because when turned, it will probably drip round the spindle. It may also be seized, and could even break. Replacements are readily available.

BTW you really ought to lag all those exposed pipes with Climaflex or similar. If they are 28mm you may have to order it, but 22mm is widely available. Use the thicker grade, where it will fit. It is easily cut with a serrated knife.

If you want to have the system upgraded, wait for the warmer weather, when people lose interest in their heating systems and the plumbers have nothing to do. I would strongly recommend having a system filter fitted at the same time, and doing a chemical clean, because an old system is likely to have a lot of sludge in it. This may remove the need for a later powerflush and reduce the risk of a blockage.

If it was me I would probably have a larger cylinder fitted as well. I can't see if yours has an electric immersion heater, which is handy when the boiler is out of action.

It's easy for me to spend your money. As minimum, let's look at the rest of the pipework. It could still be that the cylinder is scaled up inside, though that's not my first thought.

Fantastic information Piglet John. Thanks very much. Will get that other photo ASAP!

PigletJohn - You seem to know a lot about this, pls may you advise me on the best plumbing system for a home before I start amending my current one. Many people are quick to recommend a combi or pressurised cylinder but I am hesitant.
Currently it is a Vented Indirect 1050x450 with pump. The property is 4 bedroom and I'm in the process of renovating so want to make good the plumbing system before pipework is not as easily accessible.
Essentially what is the best design for a house that will demand a lot of hot water at peak times (bath, x2 showers, washing machine). And not have to wait for water to heat up.
At present I believe I should keep the same set up but replace the cylinder with a larger capacity and immersion heater.
Your thoughts would be greatly appreciated.

Haven't you got a gas boiler?

I think you ought to start a new thread, because everything up to this point relates to a situation different to yours.