Dual central heating system

Hi , I have an existing solid fuel heating system and I want to connect up an oil fired boiler to it.
Please advise on how I should plumb it, I believe I should use some check valves but not sure where they should go. Also do I need another circulating pump
thanks
Fred
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Investigate something called the Dunsley Neutraliser. Ii's just a steel box, with no moving parts like motorised valves. I have one linking a multifuel stove and an oil-fired boiler, and it seems to work well.
regards
Pat Macguire
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A thermal store is also suitable. Creates a neutral point and absorbs excess heat.
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On 6 Nov 2003 06:52:37 -0800, Fred wrote:

What ever you put into the circuit for the solid fuel boiler had best be totally passive and automatic lest you risk a big wet bang...
The boiler has got to loose the heat it gains from the fire no matter what. So the circuit really needs to be gravity driven without any requirement to operate manually or electricaly any valves. It must work without power and with minimal risk of have valves on flow and return "accidentally" shut at the same time.
Has has been mentioned you really need a Dunsley Neutraliser or equivalent.
http://www.dunsleyheat.co.uk/linkupsys.htm
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FRED snipped-for-privacy@EIRCOM.NET (Fred) wrote in message

I've got a Rayburn and a gas boiler plumbed together as follows :
First of all, the whole system is open vented. I mainly use the boiler for heating as I'm not there long enough to warrant starting up the rayburn just for 2 days a week.
I have the Rayburn with Gravity HW, and a link from this circuit to the CH. The link to the CH is in 22mm while the HW is in 28mm. The rayburn is directly under the cylinder now, but originally the cylinder was the other side of the house. It still worked then, but more by luck than judgement I think!! The boiler is fully pumped with a mid position diverter valve to do either HW, CH, or both. The HW circuit between the boiler and the rayburn is linked, with 3 port diverter valves. In the normally closed (no power) position the boiler circulates water through the cylinder, and the rayburn is isolated. The CH circuit is joined to the rayburn via the 22mm pipe. At present there are no valves on this, so the affect when the boiler is running is that the rayburn acts as a radiator. And quite good it is too!! I am considering adding some isolating valves to close this connection as well, so the rayburn is truly isolated.
When I want to run the rayburn, I flick a fused switch to open the valves on the rayburn. The boiler is powered via a standard timer, but I have an isolating switch on the boiler power circuit so that even if the timer calls for heat, the boiler won't run. The timer will however still switch the pump on, and control the mid position diverter valve. I must also ensure that the HW circuit is turned off and most importantly that the CH circuit is permanently on. The only possible down side is that the CH circuit will now circulate with the pump, resulting in the water running through the boiler. A further enhancement would be to have the boiler isolated when the rayburn is running, but only using a single pump for both CH and HW on the boiler prevents this.
Seems to work well enough, but I confess that I haven't tested it for any extended period of time. I'll do that over Christmas. All I need to learn about now is how to control the Rayburn!!
HTH David.
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On 7 Nov 2003 02:58:13 -0800, David wrote:

How isolated? is there anywhere for boiling water and steam to (safely) go? Just think what happens in a power cut with the Rayburn running, the valves shut isolate the rayburn which even if you shut it off straight away is a gert big lump of cast iron with *a lot* of stored heat and no water flow through it...
Then of course you can't run the gas boiler as you have no power but you could run the Rayburn, if it wasn't isolated...
There shouldn't be any valves in the gravity loop from a solid fuel boiler, with the possible exception of ones isolate for maintenance purposes. The gravity loop also needs to include a radiator, possibly fed via capilary action thermostatic valve on the cylinder. A solid fuel boiler is well capable of boiling a cylinder full of water and once it's boiling there is no where for the heat coming from the boiler to go other than to boil the cylinder harder and fill your loft and cold water storage tank with boiling water and steam...
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Thanks guys for all your comments, I take the point about having a gravity system. My question is if I put a check valve (non return) in the solid fuel circuit will it stop the radiator effect and what type is best the flap type or the ones with a spring to keep them closed. I want to keep it simple and avoid using any electric valves and the associated power failure problems. There is a pressure relief valve on the solid fuel boiler does this not protect against the problems stated above once there are no valves between it and the boiler
thanks Fred
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On 11 Nov 2003 01:18:18 -0800, Fred wrote:

The solid fuel loop has to operate under power fail situations ie gravity. I doubt that gravity has enough umph to open a check valve.

I guess so but I'd rather not rely on a valve that may stick and only be needed once... It also needs to be mounted at the boiler not down the end of even a short bit of 28mm pipe (IMHO) it will of course need to vent somewhere or you'll end up with a living room full of steam. The other thing to bear in mind is that if the pressure relief valve does operate is there the means for the boiler to remain full of water ie. is the cold feed is still free flowing. If not the boiler may boil dry and overheat not good...
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Fair point. I've already managed to boil the cylinder in the past, before I made any modifications to the system. Scary before you work out what the hell that violent banging is about!!
Originally I had the rayburn isolated with manual gate valves (4 in all, flow and return to boiler, flow and return to rayburn). It was a manual process to have the correct two open and the correct two shut. Also not shutting them both off at the same time, or both on (for more than the time it takes to twist the handle) as then the water would circultate in an unusual manner (possibly). As they were in the loft and I didn't fancy going up there every time I used it (however infrequently) I swapped it all for two 3-port diverter valves. Also it negates the chance of anyone else getting it wrong in the future.
I used valves that were normally shut to the rayburn as it will only rairly be used and I didn't see the point of burning out the motors to keep it shut 95% of the time. But I also (now) see your point about the system shutting down in a power cut. It is still possible to manually open the valves with the lever (I think - I'll have to double check that!). In light of what you say I will probably now keep the CH circuit as it is, without valves, as the valves were to be hidden under the floorboards in the bedroom above. Not sure I would like to be shifting furniture and lifting carpets should the worst happen and I need to manually open these valves too. Nipping into the loft during the occasional power cut isn't a hardship. Everytime I want to use the rayburn is.
Longer term, I will probably replace the cylinder with one that takes two primary circuits. It was the recommended route, and always made sense, but it was an expense I could do without at the time (and still now!). The existing cylinder is new and well insulated - if it ain't broke, don't fix it.
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On 11 Nov 2003 09:52:56 -0800, David wrote:

The Dunsley Baker Neutralizer is to avoid all this messing about with valves and flows where there shouldn't be flows etc. Having looked at the Dunsley website it might just be a sealed box to which you connect all the flow/returns for boilers/cylinders and the feed/expansion pipes. I sort of get the feeling there are no baffles etc inside. Anyone know?

It's one way but doesn't solve the CH loop problem.

Quite fit a Dunsley...
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"David" wrote | > How isolated? is there anywhere for boiling water and steam to | > (safely) go? Just think what happens in a power cut with the | > Rayburn running, the valves shut isolate the rayburn which | > even if you shut it off straight away is a gert big lump | > of cast iron with *a lot* of stored heat and no water | > flow through it... | But I also (now) see your point about the system shutting down | in a power cut. It is still possible to manually open the valves | with the lever (I think - I'll have to double check that!).... | Nipping into the loft during the occasional power cut isn't a | hardship. Everytime I want to use the rayburn is.
But what about if the power cut occurs when you aren't in the property (or possibly worse, when you are in it and asleep)?
Owain
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