No water supply, what happens when the hot water tank in the attic is empty?

[Rollerball]

I've been without any water for 24 hours (there's a problem in the area due to the recent chilly weather). The water does sometimes dribble through for a while so that's keeping the plastic storage tank in the attic topped up. I am though wondering what happens if that tank empties ? My boiler is an an oil fired Danesmoor 15 19

I'm not really sure how the system works - I assume that as the water goes via the boiler it's heated then pumped to the immersion heater in my airing cupboard?

If so, what happens if the water runs out? Naturally I don't want anything to burn out due to lack of water. Or is there some kind of automatic cut off for the heating of the water if the water runs out?

 

[Daveydub]

Heating system water and domestic hot water are completely seperate so when your cistern runs dry, central heating circuit is still full. You can therefore leave heating & water on even when domestic tank has run dry.

 

[Rollerball]

Thanks. So the cistern in the attic stores the water which is then heated by the boiler which is then stored in the tank in the airing cupboard?

What then happens if the cistern in the attic is empty? The boiler won't of course have any hot water to heat so does it automatically stop trying? (while still continuing to heat the radiators of course)?

 

[Daveydub]

The cistern in the attic stores the water which feeds the Cylinder. The cylinder supplies the hot taps. The water in the cylinder is heated with a coil which is full of system water which is heated by the boiler.
Yours may be tank fed as below or pressurised (filled from the mains). Either way, heating system remains full when cw cistern is empty

 

[Rollerball]

Noted, thanks. However, what happens to the hot water for the taps when the feed tank is empty? Obviously there's no water (hot or cold !) in the hot water taps, but is there a risk of damage to the boiler, etc if it's trying to heat water that isn't there ?

 

[Daveydub]

Running out of ways to say this.Boiler is still full of water and coil in cylinder is still full of the same water. Cylinder is in fact still full of water, not that that matters. Boiler will not be aware that it has heated a cylinder full of water which you can not use as you have no cold water in cistern.

 

[Rollerball]

Got it, thanks.

 

[TicTac]

If you ran out of water completely, the CH would still work, but the HW tank would empty, so it'd be best to change the programmer so that the HW wasn't being heated, but if it were to continue, then it'd be no different to the CH pipes under the floor carrying water round them - no danger there either.

 

[JohnD]

the HW tank would empty

I expect you mean the HW cylinder.

It would NOT empty.

The hot water to the taps comes out of the top of the cylinder, it is pushed out by cold water feeding into the bottom.

You can empty the cold water tank in the loft, or saw it up and take it away, and the cylinder will not empty.

You can turn on all the hot taps until they run dry, and the cylinder will not empty.

The boiler will only heat the cylinder until it reaches its preset temperature. Then the cylinder stat will stop it. Just the same as on any other day. It will not overheat and it will not boil dry.

 

[TicTac]

Yup, I can see your point - update appreciated.

 

[EFLImpudence]

Except - in the diagram the cylinder is called a hot water (storage) tank so the OP may not have realised the difference.

 

[JohnD]

tsk tsk.

 

[Hugh Jaleak]

If we're being pedantic, then the cylinder can be classed as a 'tank' as it's a sealed vessel. The storage feeding the HW cylinder is technically a 'cistern' not a 'tank' as its an open vessel.