How does (my) central heating work?

thor

Cardew wrote: »

When you say 'thermostat setting' do you mean the TRV setting or a conventional room thermostat?

I meant the conventional room themostat.

Cardew wrote: »

If there is no flow of water through the radiator then the pipes to that radiator will cool.

How far along the pipe does the CH send the water when the TRV is off? I had always assumed that it would go all the way to the radiator before being turned back but this can't be so and must be blocked near the boiler if the pipes do cool down.

matelodave

With a combi system you have a closed hot water circuit which feeds hot water either through a heat exchanger or through the central heating system to the radiators. There is a valve in the system which detects when you turn on a hot tap and it diverts the central heating water through the heat exchanger and turns both the pump & boiler on. This heats the hot water that comes from your taps. This is all independent from the timer circuit and will operate whether the heating system is on or off. A combi boiler cannot heat radiators and hot water simultaneously so if you run a bath the radiators won't get any heat.

To provide central heating, the closed circuit hot water circulates around the system driven by the pump which should be controlled by an external thermostat - in fact it is a requirement that you should have a thermostat which not only controls the pump but also turns the boiler on & off. The hot water circulates around the system and the TRVs control the amount of water that is bled off into each radiator - the circuit should be such that if all rads shut down then they cannot shut off the circulating water - there should be a bypass valve which returns water to the boiler so that it doesn't overheat and so the boiler stat can shut the boiler & pump off.

The best way to control a combi is with a programmable thermostat, not with a timer. A programmable stat does the work of a timer but also allows different temperatures at different times of the day and even on different days of the week. It would be very easy to install a wireless programmable stat (about £50) to control your boiler properly. Ideally the stat should be installed in a room where the TRV is left wide open, the TRVs in the other rooms can then be set to control the temperatures in each room.

If you want to get clever with remote control of the system then the programmable stat would need to be connected to your router and if you wanted to remote each room then you have to replace each TRV with an actuator which can be remotely controlled either wirelessly or via a connection to a hub, each room would need a temperature monitor which could be linked in as well - very expensive

macman

Yikes2014 wrote: »

Thank you for your reply. I think all in all its time to get someone to have a look to make sure it is operating ok.

No one can help you if you don't post the make and model. From the limited info given, it's not operating correctly and is potentially lethal if the tank is boiling. Turn the immersion off and get someone in.

Cardew

thor wrote: »

How far along the pipe does the CH send the water when the TRV is off? I had always assumed that it would go all the way to the radiator before being turned back but this can't be so and must be blocked near the boiler if the pipes do cool down.

The TRV turns off the water at the inlet to the radiator.(i.e. the TRV itself)


If there is no flow of water, the hot water in the pipe will simply cool down.


It is no different in that respect to a pipe feeding a hot water tap. When the tap has been open the pipe is hot. Shut of the tap and there is no flow of water and the pipe cools.

southcoastrgi

Yikes2014 wrote: »

I have a dumb question to ask. I don't know if the boiler system in my house is a combi system or not. I have a main gas central heating unit in the kitchen, a wall display which controls heating and water separately and then I have a large tank with two small tanks, a thermostat and a separate on/off switch on the wall in the cupboard. I thought that the switch in the cupboard was for an immersion heater and that it should only be used to boost the water for a bath etc, and that for the most part the water heating should be controlled from the main gas unit downstairs. However, my boyf reckons I'm wrong about this and the switch (which I think is an immersion) should be left on all the time to be economical. I wouldn't mind if it was left on all the time except the heat of the water it generates is completely impractical, it is far too hot (although he swears it is set at 65'C), and the tank sounds like its boiling all the time. Another opinion would be very helpful.

from your description you have an open vented conventional system (not a combi)

turn off the immersion it's only there for backup if your boiler breaks down, it's not economical at all to use the immersion to heat the hot water is gonna cost about 3 times the price compaired with using the boiler to heat the water, the cylinder stat & the stat inside the immersion should be set to 60d not 65d, if it's boiling then the stat inside the immersion has failed & it MUST be replaced (just the stat not the immersion itself)

jezebel

I've just had a new combi boiler fitted and have thermostat for the first time (before this I had a dial that was stuck on "Warm" on the boiler and temperature controlled rads)

I think I might actually be starting to understand the magic box that BG fitted for me - the man did try to explain it but it was all a bit too quick

matelodave - you are my new hero - I totally get it now

SAHD_Jim

I have a thermostat question, if someone can advise?

We have a 13 year old central heating system with a Worcester 35 CDi II RSF combi boiler and TRVs on all radiators bar the kitchen one, which I believe is required to prevent possible damage to the pump (feel free to correct!).

I have always controlled the heating relatively effectively using the TRVs, keeping rooms not used cooler and heating living areas etc to 18-21C and not overheating the house.

However, I have been aware for some time that a room stat should be more cost effective but to my shame have not got round to doing anything. I have now decided I want to get a wireless programmable one fitted.

My questions are straight forward hopefully:
1) If I have a stat fitted in the lounge or hall, can I remove the TRV in that rad and put it in the rad in the kitchen?
2) Can I use any wireless room stat or do I have to buy a specific type for this boiler. If I can use any, can anyone recommend one that would work well with this boiler for a good price?

Thanks in advance!