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A question for the heating experts


sid
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I have had a new boiler fitted under an insurance claim. We went away in February, I had drained the system but must have left some water inside the cast iron heat exchanger. When we got home, after the last very cold spell, I found that the heat exchanger had split. After visits from the insurance assessors I was informed that a new boiler could be fitted, so that's what's happened. All this is just background, because we now have a brand new Chappee boiler, which is wonderfully quiet and very fast at heating up.

So, to the questions... The new boiler works on a heating curve principle, and cycles on and off several times a day keeping the boiler water fairly hot (around 45 degrees)... (1) Is this more efficient than firing up from scratch, near zero degrees effectively?   (2) I have already a sophisticated (read VERY complicated!) controller, a Siemens RVP331 which previously ran our central heating (rads plus underfloor). I could modify the new system so that the new boiler only fires up when heat is called for. Would this be detrimental to the boiler? (After all, it's how the old one worked!).

The new boiler has its own programmer/controller so I'd be effectively by-passing this.

It's working at the moment, I just want to know the pros and cons of how it works.

Hoping for a heated debate!

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Sid, I am no expert but I can tell you that my neighbour,  who has now moved, had exactly the same boiler and heating configuration as us yet her bills were always higher. At one point we had our boilers serviced by the same guy on the same day and his explanation was that our system was set to come on once a day and stay on, (we had my elderly FIL living with us at the time )where as next doors system came on in the morning, went off at about 10 when they were all out and came on again at around 4pm in time for everyone coming home from school. It takes a lot of energy to get a system going from cold.

Hope that helps

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Hmm, thanks RH.  I don't suppose you know whether your neighbour had the room temperature higher, or whether they had the same insulation?

This new boiler has been operational for 3 weeks now. It doesn't appear to be using much fuel as I marked the semi-transparent tank when it was fired up for the first time.

At this time of year, through to autumn, we only use it for domestic hot water. I've heard all the arguments for and against using oil for this, but it works well for us and I'm not changing it. The old system was set to heat the water, a 200litre ballon, if necessary, in the morning, a top up at midday, and then again in the evening. The boiler would be completely off in between. The new system fires up to keep itself warm(!!) every couple of hours, just for about 5 minutes (I must admit I haven't stood there and timed it, but there is a counter for the number of times, and a counter for the number of hours run), and I think the idea is that because it's well-insulated it can immediately satisfy a demand for heat without having to start from zero.

To me it seems a little extravagant and I suppose I'll have to run 12 months to compare.

We generally use only around 1000-1200 litres per year. The house is well-insulated and the underfloor heating in particular has been very economical.

The point is that I could modify it quite easily to run the same as the old one, but I don't know the theory behind this mode of operation.

 

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RH, Hot water usage varies. When there's just the two of us it's first thing in the morning and later in the evening. When the family stays it's mainly around teatime.

What I need to know is whether it's harmful to the boiler to start up from cold rather than always being pre-heated.

The DHW can be set to 24/24h so that it is always topped up, or to run at specific times, or to run at the same time as normal heating programmes.

I think I have a lot of experimenting to do, but it seems wasteful, to me, to have it continually keeping the boiler reservoir warm when it probably won't be needed for a further 5 or 6 hours.

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I have found it is more economical to keep the hot water and central heating constantly on provided you have proper insulation both on your hot water tank and in your house. 

I know this may not feel intuitive  but unless your HW cools down to ambient temperture for a significant time  then you will use the same energy to bring it back up to  the proper working temperature.

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Our house in the UK was quite well insulated, not silly but cavity wall, good windows and not too much in the loft that had been converted into a room.  We found leaving the heating on as low as it would go all through the winter had no significant effect on our heating bills.

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Thank you all for the replies so far. Unfortunately I haven't got what I wanted, probably because I didn't ask the question clearly enough. I'll try again.

My query is about how the boiler works, not whether I should leave the heating on all day. Unlike UK boilers, at least in my experience, this new one doesn't simply respond to a thermostat "click". Instead it uses sensors (sondes) to monitor the room temperatures, the external temperature and the internal boiler temperature, all linked to a complicated controller with many parameters. The boiler has a heat exchanger which holds 24 litres of water. This water is constantly kept hot by the constant cycling of the burner. When the programmer calls for heat, either for a room or for DHW, the pump starts and the preheated water is circulated immediately either to the hot water tank or the room or both. The boiler then responds to the drop in its water temperature and fires up to replace the water just circulated. 

Why does it have to constantly keep heating this initial charge of water (the 24 litres), when there may be no immediate requirement, and can I adjust it so that the boiler only comes on when required even if the water in the boiler has cooled completely. Is there a risk to the boiler of thermal shock or something? This would be how it works in simple UK systems. Whilst the whole system is working now, and appears to be using less oil than the old one, I wonder if I can reduce consumption even more by not having this constant re-cycling of the boiler.

I thought there were some heating people on here; I'm sure they would be familiar with this type of operation. Chappee boilers are one of the premier French makes (part of the Baxi group).

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