Central Heating - Please explain!

[LSainsbury]

Right - will somebody here please settle a major argument between me and the GF regarding the workings of our central heating system - before she meets Pauline Fowler!

We have - a boiler in the kitchen - a tank in the airing cupboard, various radiators and hot taps of course and tanks in the roof.

The tank in the airing cupboard is not switched on.

Can you answer the questions:

a) Basically - how does water get around the system - i.e. - the boiler heats the water and is pumped around to the radiators - I know that much.

b) Why is the airing cupboard nice and warm if the tank in there is off?

c) Is water from the boiler pumped to the tank in the airing cupboard and hot water is drawn from that?

d) What exactly does the thermostat in the hallway control?


Need a domestic heating systems #101!

Cheers

Lee

[superbiatch]

Is it a combi-boiler? Cos if it is my understanding is that you don't have a tank and the water is heated in the pipes. Not sure how correct I am in my thinking, but i used to have one with no tank (as it was a new house)

[LSainsbury]

It's one of these....not sure 100% - but we think it is.

When you say the tank in the airing cupboard is 'not switched on', I'm guessing you mean it is fitted with an immersion heater which is not switched on. Before we had central heating, the immersion heater heated the water in the tank, providing hot water. When the central heating was installed, the same tank was used for hot water, but the water was now heated by the central heating bolier, making the immersion heater redundant. We have since had the tank replaced, and the new one does not have an immersion heater.

[Ramrod]

The airing cupboard is hot 'cos it's got a hot water tank in it, the water gets round via a pump.....

c: I believe so
d: It controls the temp that the central heating runs at?

[Escapee]

Originally Posted by lsainsbury

It's one of these....not sure 100% - but we think it is.

That looks like a Combi to me.

I am no expert, but it sounds like you do not have a combi boiler. theCombi does not use a tank, it contains its own pump and directly heats the mains cold water as it passes through to produce hot water.

The system you have is probably connected to the tank in the airing cupboard, and the boiler pumps water around the radiators for heat. It also pumps water to the hot water tank in the airing cupboard where the hot water is stored for use. When you say the tank is warm but turned off, I guess you are saying the mains switch to the tank is truned off?

Tanks usually have an immersion heater (like a kettle element) to heat with electricity if the heating is off and you need hot water for a bath etc. The heat from the tank is from the gas boiler if the immersion is off.

The thermostat probably controls the on-off switching of the boiler, and would probably have no effect on the immersion heater that usually has its own element.

I am far from an expert, but hope some of my info helps.

PS: The hot water in the tank is not directly heated by the boiler, it heats mains cold water that enters via a stop valve. ie. The boiler water and washing water are in seperate compartments of the tank.

The water gets round the radiators via a pump, but (at least here) you can turn off the central heating (which switches off the pump) but still have hot water - I assume the water circulates from the boiler to the tank by convection.

[Wicked_and_Crazy]

a) Basically - how does water get around the system - i.e. - the boiler heats the water and is pumped around to the radiators - I know that much.

The water that flows through the bolier will also flow through the radiators and the hot water tank

b) Why is the airing cupboard nice and warm if the tank in there is off?

what do you mean by the tank being off? The tank if insulated well will keep the water hot for a couple of days. Also your pump and valves are likely to be in there too. If your pump is in there its likely all your hot water from the boiler goes to the airing cupboard before being distributed around the radiators.

c) Is water from the boiler pumped to the tank in the airing cupboard and hot water is drawn from that?

The heated water from the boiler goes through a coiled pipe that runs through the hot water tank. If you look at the tank it will have 4 pipes connecting it one from your boiler and a return, the other two are from your water tank in the loft ie you cold water in and one to the taps ie your hot water out. The stored water that is in your hot water tank is heated by the hot water from you boiler flowing through the coiled pipe in the tank transfering heat

d) What exactly does the thermostat in the hallway control?

Room temperature and therefore the flow of water through the radiators. The thermostat switching on and off causes a valve to move which either lets hot water from the bolier through your radiators or stops it.

[mr_bo]

Originally Posted by lsainsbury

The tank in the airing cupboard is not switched on.

Can you answer the questions:

a) Basically - how does water get around the system - i.e. - the boiler heats the water and is pumped around to the radiators - I know that much.

b) Why is the airing cupboard nice and warm if the tank in there is off?

c) Is water from the boiler pumped to the tank in the airing cupboard and hot water is drawn from that?

d) What exactly does the thermostat in the hallway control?

If it is like my system then:-

a) the water is pumped through the boiler then to a valve which determines if the hot water or radiators or both are switched on at the timer panel. If just the rads are on then the valve directs the hot water to a manifold then on to the rads. If the hot water is on the water is pumped ino the tank in the airing cupboard but it does not mix with the tap water as it is fed through a coil of pipe in the tank, works like a kettle element but without current in the element just hot water.

b) you mean the immersion switch is off? this is like a fall back so you still have a heater in the tank to heat the water electrically if you have a boiler problem or some other failure like gas supply.

c) see a above

d) the temperature that the boiler heats the water to

[Wicked_and_Crazy]

Originally Posted by mr_bo

If it is like my system then:-


d) the temperature that the boiler heats the water to

wrong

The thermostat in the boiler will set the temperature of the water that makes the bolier flame cut out. The thermostat attached to the hot water tank sets the temperature at which the hot water stops being heated. The wall thermostat sets the room temperature for the house as the radiators most likely have their own regulators (unless they were added later)

[mr_bo]

Originally Posted by Wicked_and_Crazy

The wall thermostat sets the room temperature for the house as the radiators most likely have their own regulators (unless they were added later)

And how does it achieve this?

[Wicked_and_Crazy]

Originally Posted by mr_bo

And how does it achieve this?

By controlling the 3 way valve. Most systems have a single valve or two vales that direct the heated water from the boiler via the pump into the valves.

One outlet will go the the hot water tank, this is controlled by the thermostat on the hot water tank

The other outlet will go the the radiators and is controlled by the wall thermostat.

So as you say you can have water flowing into the hot water tank, or the radiators or both (depending on temperatures and the setting in the controller.

How does the thermstat do it? its a bimettalic switch or a wax thermostat that makes or brakes the electric circuit controlling the valve.

[LSainsbury]

Thanks people!! The GF was correct (again) ...bitch...



I thought the water was stored in the boiler until drawn off...but then again it would be a bloody small space to store 3 baths full of hot water! Stupid me...

I think my confusion is in my old house, we only had an immersion heater that heated the water.

Thanks for the domestic #101!

[Angua]

Or if you have a faulty valve you can have the central heating off and still get hot radiators

There should be a timer that determines which part is on at any one time depending on how sophisticated this is determines which part of the heating system is on at any one time. On a basic one you can have water heated without central heating or vice versa but if they are both on, they are on at the same time.

[mr_bo]

My system does not have a wall thermostat, just a two way valve, rad thermostats and a froststat next to the boiler in the garage but the higher the froststat is set to then the longer the boiler runs consequently heating the water more - obviously governed by the boiler thermostat which I forgot about