How exactly does a gas boiler work?

ally18

Sorry this will appear to be a daft question but I would like to ask opinions on here before I go back to my plumber.

In May this year I had a combi condenser boiler installed with a thermostat put in the hall. This replaced an old baxi boiler that just switched on and off.

Now, yesterday evening I switched the boiler over to heating for it to come on and it was wonderful. With this being new to me though, I was constantly watching the thermostat to see how it increased. It went fine from 16d to the set temp of 18.5d in about 2 hours. I expected the boiler to then switch its self off as it had reached temp but it carried on running, although the temp didn't increase.

I understand the boiler will then keep the temp constant by switching on and off (I think) but the noise from it was constant, it didn't seem to switch off at all as far as I could tell. I have looked through the instruction booklet but it doesn't explain anything. How high do you set it as well? The plumber set the temps at 55d for water and 75d for heating. I know how to alter these but then when the boiler was 'firing' so to speak, it went up to a 6 and later when the temp was achieved, it came down to 3. Is this a scale for the burner?

I've been used to a basic noisy boiler before so this is a novelty. Sorry if this is a daft question

tanith

It could be something simple like having the boiler set to 'constant' for either the water or heating.. have you checked?

daveyjp

75 degrees is probably maximum. The boiler will fire to maintain this temperature in the heating loop, hence you seeing a small burner symbol.

Turn it down to say 65 and see what happens.

55 for water is also quite high. You are heating water to a temp where cold water is needed to cool it down, thereby wasting energy.

ally18

Thanks for your replies.

No, I can clearly see the dials for timer, heating on constant or heating off as this is a little button where the clock is on the boiler. I had it set to heating off since May and only last night switched it over to heating on.

The plumber did say that 55d is the setting water has to be at due to legionaires disease so I haven't changed this. I have come across this at work, they are forever checking the water temp.

Since May though, the boiler has been coming on at intervals for about 5 seconds. I was told that this was the boiler heating up the small tank of water contained inside the boiler. This was to give you immediate hot water when the tap is turned on. I can't find anything mentioning this in the manual. In fact it doesn't tell me a lot apart from how to increase/decrease the heating and water temps and to recognise error codes!

ally18

Just to add, I checked the gas reading back in July due to moving supplier and the reading was 2468.
Yesterday before I switched the heating on it was 2476 and when switched back off 2478. 2 units for 3 hrs use. 20 since 15 July.

Plus I have a gas cooker which is used every day. I guess I shouldn't worry about it heating that tank of water as it isn't that much is it?

daveyjp

What boiler? The is probably No need for pre heating to be on.

ally18

Its a Remeha Avanta Exclusive 28w with a Qstat thermostat

riverstyx

The risk of legionella with a combi boiler is very low although I suppose if you have a combi that does store a small amount of heated water there might be a very slight risk.

Please post the make and model of the boiler and the make and model of the thermostat so we can advise appropriately.

Generally modern boilers will burn more gas when they first fire, until the water in the system reaches the temperature you have selected on the front panel, they will then reduce their gas consumption to a lower level to try and maintain this temperature (this is what the 75 degree setting relates to - it's the temperature of the water being pumped out to you radiators).

Also, the thermostat will call for the boiler to fire when the room temperature is below what is selected, and instruct the boiler to stop firing when the room has reached the desire temperature (obviously until the room starts to cool again, at which point this cycle will repeat).

Some modern boiler / thermostat combinations are a bit more intelligent than this though, and the thermostat can actually control how much gas the boiler burns in relation to how much difference there is between the desired room temperature and the actual room temperature (this is referred to as temperature compensation), and some go even further by also adjusting the burn rate according to the outside temperature (called weather compensation).

All of these features if fitted are really designed to try and keep the room temperature much closer to what is desired, as opposed to overshooting the selected temperature, waiting for the room to cool, then overshooting it again and so on.

The pre-heat function if it has one, does tend to burn a little gas and can usually be turned off or sometimes even put on a timer. If you're not at home all day for example, and only draw water mornings and evenings, it probably doesn't make sense to leave the pre-heat switched on all day (it will save a little water when you run the tap waiting for hot water, but at the expense of burning a little more gas)

Hope this helps,
Martin.

riverstyx

ally18 wrote: »

Its a Remeha Avanta Exclusive 28w with a Qstat thermostat

Ok, I see you have responded whilst I was writing my reply, I'll take a look and see if I can work out how this setup works and whether it is possible to turn off the pre-heat.

Kind Regards,
Martin.

riverstyx

ally18 wrote: »

Its a Remeha Avanta Exclusive 28w with a Qstat thermostat

Ok, I think it must be a 'Qsense' rather than 'Qstat' thermostat as this seems to be what comes supplied with these boilers.

This is one of the more intelligent thermostats that communicates with the boiler rather than just telling it to turn on and off. You can also use the thermostat to turn off the hot water pre-heat function of the boiler by turning on eco-mode.This should result in a tap symbol with a line through it near the top right of the display.

I'm assuming you have the manual for the thermostat but it appears to be a case of holding down the button for three seconds, then finding the eco-mode function in the menu.

Hope this helps, let me know how you get on.

Martin.

ally18

Riverstyx,

Thank you so much for your replies, I'm sorry I didn't have chance to read them until this morning.

I have read something about the eco-mode function but it wasn't clear that that was what it was for. I'm not in during the day so it would be best for this to be turned off. I will have a look at it tonight when I get home.

Again, many thanks for the explanation. It is much clearer now.