Hot water coming on with central heating?

faithlehane

This might be the dumbest question ever but please bear with me - I’ve never had central heating and my Google fu is failing me. I will contact my letting agent obviously if there is an issue.

Just moved house. Tried out the central heating yesterday, radiators heated fine. The hot water was definitely off (and definitely has a separate control), yet I ended up with a full tank of hot water. I thought that the central heating system was separate to the hot water tank and that the boiler heated the water as it ran through the radiator circuit. Am I wrong or is it broken? Seems inefficient to heat the tank as well.

As a side note, having the hot water on does not heat the radiators - I’ve seen lots of threads about that issue and it being the valve.

More info: I have a condensing boiler downstairs and the hot water tank is in the airing cupboard upstairs. The tank is one of those newer ones with the hard coating instead of the fluffy jacket. The boiler is a Worcester, I have no idea when it was installed but it doesn’t look ancient. They serviced it last week and that was fine. The controls for it all are a decrepit thermostat and one of those programmer boxes that has hot water on the left and heating on the right and the various options. The open vented diagram in here is what I think is going on with the overall system as there are pipes into the loft and I can see the valve and the pump: won't let me post the link, it was on the APHC website.

Ebe_Scrooge

My first thought was going to be the diverter valve, but you seem to have already covered that one.

Is there an immersion heater that's been left switched on ? Quite often there's a separate electric immersion heater to be used as a backup if the boiler breaks down. There should be a switch for it somewhere, check that it hasn't been accidentally switched on.

faithlehane

Thank you The immersion is definitely off. The issue is that having the heating on made hot water - not that there's always hot water. Could the valve be broken only one way?

RelievedSheff

The boiler in our old house which had a separate hot water tank also heated the hot water when the heating was on. The two options were hot water only or heating and hot water.

I believe this is fairly typical and it never proved a problem in the 12 years we lived there.

We have a combi now so only heat water as we need it which does seem to be saving us a lot of money on gas.

pramsay13

My system is as RelievedSheff describes.

The boiler heats the water that goes through the radiators heating the house, and then that water ends up in the tank to be used for washing dishes, shower etc.

If we have hot water on only the heated water bypasses the radiators and goes straight to the tank.

It's not possible for us to have only central heating on, it's either HW only or HW / CH.

twopenny

I have had 2 systems in 2 houses that were straight forward gas boilers and it's pretty much the same as Relieved said. I think the old one with the controls attached to the boiler I could turn temperature of the hot water down so it didn't heat but not with the white control boxes.

It's hot water only or Ch and hot water. Didn't know there was any other way.
The white control you mentioned I've had in both places. The first had a button that bought either HW or CH just for one hour. That was really useful as an override and kept the usage down in the shoulder months.

The current one in the new place brings whichever pressed to the end of the programmed session - so longer. I'm still trying to get the programming right and going to get the one hour one to replace it.
Will be interested to see what people say

Carrot007

pramsay13 wrote: »

The boiler heats the water that goes through the radiators heating the house, and then that water ends up in the tank to be used for washing dishes, shower etc.

Surely not, the heating is a closed system.


Who want rusty crud filled water to wash with?

onomatopoeia99

Carrot007 wrote: »

Surely not, the heating is a closed system.


Who want rusty crud filled water to wash with?

There will be a loop in the hot water tank that the water heated by the boiler runs through and this heats the water in the tank.

neilmcl

pramsay13 wrote: »

My system is as RelievedSheff describes.

The boiler heats the water that goes through the radiators heating the house, and then that water ends up in the tank to be used for washing dishes, shower etc.

If we have hot water on only the heated water bypasses the radiators and goes straight to the tank.

It's not possible for us to have only central heating on, it's either HW only or HW / CH.

That's not how it works at all, water between your central heating system and DHW is not mixed. What you may be confusing is an indirect boiler system where the central heating pipes enter the storage tank and indirectly heat the hot water via a heat exchanger.

There is a type of system found on quite old installations known as a Primatic system where both DHW and the heating system are fed to to the same cylinder/tank but are kept separated by a trapped air bubble but these are a pretty rare sight these days.

faithlehane

neilmcl wrote: »

What you may be confusing is an indirect boiler system where the central heating pipes enter the storage tank and indirectly heat the hot water via a heat exchanger.

Thanks for all the replies - this bit has suddenly made sense to me, I think that was the gap in my knowledge about how the tank works. So from what everyone has said: when the central heating is on it goes through all the radiators and a pipe inside the tank - so the stored water gets indirectly heated using some magic in there - but when the hot water is on alone that valve shuts off the central heating part and the bit inside the tank still heats.

Side note, is a very small amount of water dripping from the bottom of the boiler a major issue or just condensation? It's from the pipe that has a CalDensate thing on it.

Thank you for bearing with me!!