Input water temp of combi boiler

[biggmw]

Good evening to all you well educated peoples out there.

I have a Worcester 240 boiler, running on lpg.

The system works fine and is obviously a pressurized system running 15 radiators.

Am I correct in thinking that the boiler works on the principle that the "outflow" through the heating side is controlled to a set temperature, and therefor if the "inflow" was already at this temp the burner would shut off leaving the pump running?

Likewise for the DHW if the inflow from the mains was already at the set temp would the burner not run?

This would sound like an odd question but I am coming from the thought that I could add two heat exchangers to the system, before the boiler on the ch circuit and on the inflow of cold dhw.

These exchangers could then heat the system from an open vented wood fired system, with heat store capacity.

If the boiler would react as I suspect then the boiler would basically control the heating and dhw as normal, with the advantage of only firing when "needed", ie when heat was not available from the wood fired side.

I look forward to your replies, as to whether it would work,and if it is a possible solution.

Would rather get my ideas right now before I contact anybody with regards to installation.

Cheers

Gordon

 

[muggles]

Err well the combi is on a pressurised sealed system, and you can't have sealed and open-vented running into the same radiators, so I don't quite see how you would make this work. You'd need bloody huge heat exchangers to extract enough heat from your woodburner to transfer it to the heating system without having the two linked in any other way.

If you try to use the woodburner to heat your DHW you'll have it at an uncontrolled temperature, and the only pressure relief would be when someone opens a tap. Heating the mains is just a general no-no, the heat will creep back into your mains system and could cause health issues. Bad idea, sorry

 

[biggmw]

Thankyou for the swift reply.

I am not meaning the ch system to be interrupted in any way, simply heat added through a heat exchanger, all be it as you say a helluva big one, these are available however I believe for the very purpose of adding heat only to a pressurized system.

As far as the hw goes I was meaning again to have the hot water from the boiler NOT hydraulically linked to the cold water, simply flowing through a heat exchanger again.

The heatsource, being the woodboiler, would be combined with a thermal store, therefor the temp of this would be reasonably constant.

basically I am wishing to add heat to the existing system ,without altering it.

Would the combi act a I imagine though as that would be the important factor, ie only firing when the temp is below a set threshold on the input side?

Best Regards

Gordon

 

[muggles]

It could work if plumbed in the way you describe, although even dry-connecting the mains is an issue as you'll still be introducing heat to it downstream of the boiler and you shouldn't do that.

What exactly are you attempting to achieve, ultimately, here? If it's a cost saving then I'm afraid you're going to be sorely disappointed, setting all this up will be very very expensive, and it will almost certainly look hideous too

 

[mickyg]

you can fit a heatstore that has coils for your wood stove and your boiler to heat it, with priority to the stove. Output from the store to the rads and another to a plate he for the hw. Only problem is you can't preheat water into most combis including yours, its a recipe for scalefest 2009. I'd forget this part of your plan if ive understood it correctly.

 

[muggles]

you can fit a heatstore that has coils for your wood stove and your boiler to heat it, with priority to the stove. Output from the store to the rads and another to a plate he for the hw. Only problem is you can't preheat water into most combis including yours, its a recipe for scalefest 2009. I'd forget this part of your plan if ive understood it correctly.

Hmm now there's an idea, good call. You could even just plumb in a twin-coil cylinder and use that as a HE. Will still be expensive though

 

[biggmw]

Thankyou all for the replies so far,

From what you are saying the dhw is the problem but my think is correct about the combi shutting the burner off when the ch circuit is returning at the temp required.

As far as dhw goes would the exchanger post the combi be the option, and manually turn the dhw off on the combi?

As far as what I am wanting to do, I am ideally looking to power the heating and dhw from the woodboiler. The boiler will be outside in a workshop and minimal disruption of the existing system is GOOD...

The combi I would like to retain for purposes of backup, ie when the fire is out.

The option of combi heating the store is also one I am looking at but that would involve a lot more rerouting of pipework etc.

Best Regards

Gordon

PS we are in Scotland a with lovely soft water