Chappee Condensing Boiler - Flame on all day

[GillObrien]

Hi all,

We have a Chappee condensing boiler, Luna Platinum 3.25 HTE, 45L hot water cylinder, fitted in our house (which is around 110 sq m, 4 bedrooms and not that well insulated). The boiler has gas adaptive control and we have an external temperature sensor as well as an internal one. The radiators are not new, and are a mix of old steel, column style radiators and 1980s flat panel ones. We have double glazing throughout and the loft has been converted and is insulated to 1970s standards. We heat the house to around 19.5 degrees in the warmest part, so the loft and bedrooms are around 18.5 degrees. We are south facing so get a lot of heat from the sun.

I am not sure what info is useful, but I know that the settings on the boiler are standard, so the heating curve is set to the correct one for the local conditions and the water is at 55 degrees. I also see the following when the flame is on:

Boiler temperature: 41 degrees (it was about to go off at this point so I am not sure what it is when it is in full flow)
Set temperature boiler: 43 degrees (this goes blank when the heating is off so I am not sure what this is)
Return temperature: 37 degrees

It has two flames, and I only ever see the second one come on after we use the hot water for the first minute of reheating the cylinder. After that it just switches to the first flame, which is lower.

I know the boiler is condensing because I can hear the pump regularly pumping the condensate to the drain.

My question is, on colder days the flame 1 seems to be on most of the day at a low level, rather than going on and off. Is this normal and correct? Our old boiler used to blast out for an hour or so then go off for a while and come back on every so often and the radiators were boiling. Now the radiators are cooler, which is much nicer in terms of heat. This morning, as it is not that cold (11 degrees outside at 10am), it was on from 6am to 11am non stop to reach the desired temperature. The most gas we ever used in one day was 67kWH and we average around 40kWH.

We still use much less gas than with the old system, but I would like to understand if we have everything set up optimally. The installer did check all the settings, and he did tell me that he was happy to come back once we had been using it for a while and check the settings were optimal. We haven't had a lot if winter use yet, so I am waiting to have a full winter and he can look when he comes to do the the service.

Any feedback is interesting for me (I know we should change the radiators and insulate the loft, but these will be done over the next year or two along with other work).

Thank you!
Gill

 

[JonathanM]

I am not sure what info is useful

Is this property in the UK?

 

[GillObrien]

No I am in France.

 

[Ltnman]

Low temperature heat that is on for longer is more efficient than high temperature on off heat.

 

[JonathanM]

It has two flames, and I only ever see the second one come on after we use the hot water for the first minute of reheating the cylinder. After that it just switches to the first flame, which is lower.

Where are you seeing the flames? Do you mean you are seeing an actual physical flame? Or the image of a flame on the display panel.

We have a Chappee condensing boiler, Luna Platinum 3.25 HTE, 45L hot water cylinder

Is that 45L cylinder inside the boiler? Is it a combi boiler with internal hot water storage?

Is this your boiler?

https://www-chappee-com.translate.g...tr_sl=fr&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=sc

 

[JonathanM]

If so, it looks like it can cut its power right down to 2.4KW, which is very low. Maximum 25KW, minimum 2.4KW.

 

[GillObrien]

That is my boiler.

I can see the two flames either on the boiler itself (it has a green light for each flame and when they are on it is lit) or it also tells you on the detachable control unit which flame is on. It can either be 1 or 1 and 2, not 2 only.

The cylinder is in the boiler. I don't really understand how the hot water works. In theory you never run out, it keeps the 45l hot so you have instant hot water but it is capable of reheating as you use it. We have never had it go.cold. In theory you can also take two showers at once, but that doesn't work here because of something to do with debit and the pipework.

My understanding was that yes, it can regulate very low, so can be efficient.

We are happy with it, although it would work even better if we had newer radiators and enough of them. I am just curious with question of whether the low flame on all day, or a lot of the day, if really more efficient than it coming on an off throughout the day at a higher level.

Thank you for your responses!

 

[JonathanM]

I am just curious with question of whether the low flame on all day, or a lot of the day, if really more efficient than it coming on an off throughout the day at a higher level.

Running at a lower temperature, for longer, will be the most efficient way in terms of the amount of gas burnt. That's because the lower the return temperature, the more condensing you will get. Below is a graph, which somebody posted earlier today, showing how efficiency increases as the return temperature decreases. If you ran it for shorter periods, the boiler temperature would have to be higher, to keep the house at the right temperature, and so it would be running less efficiently. Overall you would be producing the same amount of heat, it's just that the first way takes less gas.

There is a slight question, I suppose, of whether running so many hours uses more electricity, because the pump is running for longer. But modern pumps are very efficient, and they will usually run at a very low power, when the boiler is also at very low power.

It sounds like you have weather compensation, where the boiler chooses its own temperature based on the external temperature, rather than you setting the boiler temperature yourself? I was a bit surprised that the difference between the flow temperature and the return temperature wasn't bigger. It's only 4 degrees. The bigger the difference, the lower the return temperature, and the greater the condensing. But that might be because you say you don't have enough radiators? Also, did you say the boiler had just turned off when you took those readings?

EDIT: The most efficient way to run the boiler might be different if the house isn't occupied during the day.

 

[JonathanM]

Just following on from the above, there might be a way of improving efficiency even further, if that difference between the boiler flow temperature and the boiler return temperature could be increased. You would need to check those numbers again, when you are sure the boiler is still running, rather than when it might just have cut off.

There is a rule of thumb, that the difference should be about 30% of the flow temperature, for best efficiency. So, say the boiler temperature actually is 41 degrees as noted above, then the difference should be 12.3 degrees. So you would be looking at getting the water returning to the boiler at 29 degrees or below, rather than the 37 degrees you have. If you use the above graph, you can see that would increase the efficiency from just over 94% to just over 96%.

But you would need to check those boiler flow and return temperatures first, before deciding if you wanted to try to do anything about it. It might involve balancing the radiators, or slowing down the pump, or both.

With all of this, I still find it counter-intuitive that running the boiler for such long periods can actually be cheaper!

 

[GillObrien]

Yes, we have weather compensation, so I think because it is not cold the boiler is not so hot. I checked again and it was still showing 41 degrees.

We don't have enough radiators, we have nine for the whole house, so one per room. However, two of the rooms are between 25 and 30 sq m and have one radiator that is 75cm wide. These are the largest ones we have, the others are between 40 and 50 cm x about 80cm tall. So we need to replace them at some point and add a couple.

It will be interesting to see what happens when the outside temperature drops lower.

Thank you - I am reassured!