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
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.
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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
Dave. pam is missing e-mail
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!!
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...
Dave. pam is missing e-mail
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
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...
Dave. pam is missing e-mail
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.
<snip> Tale of many a valve in inaccessable locations...
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.
It's one way but doesn't solve the CH loop problem.
Quite fit a Dunsley...
Dave. pam is missing e-mail
| > 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)?
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