Basic question on central heating with combi boiler

Dedekind

I am having a new combi boiler fitted but the question applies anyway with old boilers as well.. just want to know what people usually do.

Property has: 6 radiators with TRV (with the last setting being the 'snowflake' symbol) + one with manual valve + underfloor heating in one room. 

Will have one room thermostat in the hallway (nest). 


I am used to turning off the heating during the night and whenever I leave home. 

Should I leave the 'heating' selector in the boiler always on and decrease the temperature overnight/when away with the Nest thermostat? I read something in the boiler manual about leaving heating always on for frost protection but it sounds a bit extreme. 

Also, apart from rooms that are purposely left unheated, is there any use for the snowflake setting in the radiators? I'd like to avoid turning the TRVs as much as possible after initial setup to make life easier.

Sorry if this is too basic! Thanks 

vic_sf49

I leave my boiler on, and just control it all via the thermostat (Hive in my case).

I have the temperature set low enough over night (14 degs) that the boiler is unlikely to fire up, except when it's extremely cold maybe twice a year. 

Can't answer ref the rad trvs, as mine (old manual style) are all set between 3 and 5 (fully on).

Norman_Castle

https://www.traderadiators.com/blog/thermostatic-radiator-valve-numbers

The numbers on the valve roughly correlate to the room temperatures below. When the room drops below these temperatures, the TRV will allow hot water to flow into the radiator:

• 0 = Off
• * = 7°C
• 1 = 10°C
• 2 = 15°C
• 3 = 20°C
• 4 = 25°C
• 5 = 30°C

A fully functional TRV will detect the temperature of the room and automatically adjust the amount of hot water in the radiator accordingly.

During the winter, you should really set your TRV to 2 or 3 and leave it. If you go into a room that's cold and the radiator is burning hot, leave it alone and don't turn it up to 5. Let it do it's job and allow the TRV to heat the room accordingly.

(If you're away for a long time in winter, set your TRVs to * so that the rads will come on for a short while if the temp gets below 7°C)

----------------------

I'd add to the above the default setting should be 3, about 70 degrees. Once the heating has been on for a few hours adjust in small amounts to suit the required temperature in that room. Ignore the current radiator temperature. If the radiator is cool the trv is doing what it is designed to do, limiting that rooms temperature to the set amount, once the temperature drops below the setting it will open to allow the room to be heated.

They're also either open or closed, they don't reduce the flow so setting them at a lower temperature doesn't effect how quickly a room will heat from cold.

Dedekind

Norman_Castle said:

https://www.traderadiators.com/blog/thermostatic-radiator-valve-numbers

The numbers on the valve roughly correlate to the room temperatures below. When the room drops below these temperatures, the TRV will allow hot water to flow into the radiator:

• 0 = Off
• * = 7°C
• 1 = 10°C
• 2 = 15°C
• 3 = 20°C
• 4 = 25°C
• 5 = 30°C

A fully functional TRV will detect the temperature of the room and automatically adjust the amount of hot water in the radiator accordingly.

During the winter, you should really set your TRV to 2 or 3 and leave it. If you go into a room that's cold and the radiator is burning hot, leave it alone and don't turn it up to 5. Let it do it's job and allow the TRV to heat the room accordingly.

(If you're away for a long time in winter, set your TRVs to * so that the rads will come on for a short while if the temp gets below 7°C)

Got it. If I didn't have a thermostat and only controlled things through the boiler, for this to work I need to have heating on all time. Will the boiler be heating water even if all the TRVS are off?

Norman_Castle

Dedekind said:

Norman_Castle said:

https://www.traderadiators.com/blog/thermostatic-radiator-valve-numbers

The numbers on the valve roughly correlate to the room temperatures below. When the room drops below these temperatures, the TRV will allow hot water to flow into the radiator:

• 0 = Off
• * = 7°C
• 1 = 10°C
• 2 = 15°C
• 3 = 20°C
• 4 = 25°C
• 5 = 30°C

A fully functional TRV will detect the temperature of the room and automatically adjust the amount of hot water in the radiator accordingly.

During the winter, you should really set your TRV to 2 or 3 and leave it. If you go into a room that's cold and the radiator is burning hot, leave it alone and don't turn it up to 5. Let it do it's job and allow the TRV to heat the room accordingly.

(If you're away for a long time in winter, set your TRVs to * so that the rads will come on for a short while if the temp gets below 7°C)

Got it. If I didn't have a thermostat and only controlled things through the boiler, for this to work I need to have heating on all time. Will the boiler be heating water even if all the TRVS are off?

No, the boiler will know when to produce heat, even when running its often only intermittently producing heat. Mine often shuts down completely, including the fan and and pump if no heat has been needed in the previous 10? minutes. It'll start up again once the thermostat tells it heat is needed.

NSG666

As you are having a new boiler, hive and UFH installed I'd fully expect the installer to go through the controls for each with you as well as the topping up the pressure procedure for the system.

The UFH will/should have it's own controller and thermostat independent of the one that controls the rest of the house and once the boiler has been commissioned and the system is set up you shouldn't need to adjust anything on the boiler directly just control the heating via the programmable thermostats.

Dedekind

Thanks all. Also due to this being part of a larger renovation, we will have the boiler without the thermostat for the next 3 or 4 weeks until the electrician comes again. 

In the mean time, would it be fine to leave the heating on the boiler ON all the time and control the actual heating via the TRVs? 

Bendy_House

Dedekind said:

Thanks all. Also due to this being part of a larger renovation, we will have the boiler without the thermostat for the next 3 or 4 weeks until the electrician comes again. 

In the mean time, would it be fine to leave the heating on the boiler ON all the time and control the actual heating via the TRVs? 

That would 'work', but is not an ideal solution (and is against regs). If the TRVs shut down due to the rooms reaching their desired temp, or due to being manually turned down by you, then the boiler would find itself not being able to distribute the heated water within it. It would therefore 'modulate' down to produce the lowest amount of heat possible (like turning down a gas hob ring), and when even this is too much, would shut off the burner completely, whilst still keeping the pump and everything else running.

So, yes, it'll sort itself out and should be fine.

One important point is that one rad should be 'manual' valves only, and should always allow some water to pass around the rad circuit - ie it shouldn't be turned off. This is called a 'by-pass', and is important for the boiler. Most (all?) modern boilers will actually have an 'auto by-pass' built in to them just in case someone were to shut off all the rads, but it's best not to rely on this, so make sure one rad remains 'manual' and at least partially open.

Clearly not having a room 'stat is 'not a good thing', as the boiler will be trying to work all of the time. But, some folk do run their CH's like this.

As someone has pointed out, UFH should really have its own 'stat control - doesn't yours?

And one more thing, when you do have a room 'stat fitted for the 'rads' part of your circuit, the rads in that room should be the 'manual' ones, so always open a fixed amount to provide the right amount of heat to that room, whilst also matching the needs of the rest of the house. Ie, the 'manual' rads in the room which has the 'stat, should be outputting heat at a rate that is close to the other rooms, so that when the 'stat goes off, all the rooms are quite happy.

NSG666

Dedekind said:

Thanks all. Also due to this being part of a larger renovation, we will have the boiler without the thermostat for the next 3 or 4 weeks until the electrician comes again. 

In the mean time, would it be fine to leave the heating on the boiler ON all the time and control the actual heating via the TRVs? 

I don't know why the plumber can't wire in the hive when the boiler is installed then the electrician can work his magic later. you don't wan to leave the boiler on 24/7 without a thermostat.

Dedekind

NSG666 said:

Dedekind said:

Thanks all. Also due to this being part of a larger renovation, we will have the boiler without the thermostat for the next 3 or 4 weeks until the electrician comes again. 

In the mean time, would it be fine to leave the heating on the boiler ON all the time and control the actual heating via the TRVs? 

I don't know why the plumber can't wire in the hive when the boiler is installed then the electrician can work his magic later. you don't wan to leave the boiler on 24/7 without a thermostat.

Yeah I'll push him a bit to install the receiver. The stat itself is wireless and can be plugged in to a mains socket so..