Connecting a Hunter Herald multifuel stove into central heating system

[Academan]

I have a Hunter Herald 14 multifuel stove with a clip-in boiler. The stove is connected to the central heating system by a simple connection with a valve.
The boiler is connected to a traditional open system (Worcester condensing oil 18/25 boiler), a twin coil cylinder with the second coil connected to a Navitron solar thermal system. Cylinder is on ground floor and most of the pipework is in the eaves upstairs.
Our current plumber says that we should separate the two systems as there is sometimes overflow of hot water in the loft when the central heating system is on (corrosion risk).
I did discuss the original system with the previous plumber and suggested a Dunsley neutraliser but he said it was not necessary. Can anyone give me advice on what to do?

a) separate the two systems (put in more radiators connected to the stove only)
b) get a Dunsley neutraliser (cost implications for changing pipework, which model etc.?)
c) just run the stove without a boiler

Many thanks for any advice would be appreciated


Academan

[sleepybubble]

Presuming that the Stove gravity cylcles for DHW and the pump only comes on for heating when the DHW is stisfied by a Cyl stat, sounds like you are suffering pumpover. DO a search on here for the word and you'll find numourous discussions on it. You may find that all is required is the relocation of the pump on the pipework with relation to the vent and or F&E pipes.
Give us an idea of the sequencing... i.e. is it stove/Vent/F&E/Pump or is there some control valves etc.

[Tigger]

I've just installed a Herald 8 using a Dunsley Neutraliser (mine was the R type but not by choice, I did a swap with a friend who had one he was no longer using) and it does a great job of hooking up my oil boiler and WBS.

Plus points:

Very flexible, using the configuration from Dunsley I can just use the WBS and as soon as the Hot Water Cylinder is up to temp then it closes off the feed to the cyl and sends the heat around the central heating system.

If necessary I can run the oil boiler at the same time so that the oil boiler fills in the gaps where the WBS doesn't provide enough heat.

Operation of the oil boiler on it's own is unchanged.

Minus points:

I now have a big heat source in the airing cupboard.  The DNV is effectively a steel box full of hot water so it now acts like a radiator.  I need to get some insulation around it since it also allows heat to leak from the HWC via the boiler coil overnight.

There is only CH programmer that can be used with the standard Dunsley wiring set up.  It's a simple Danfoss (that should have said Honeywell ST699) which doesn't allow things like a one hour boost to DHW or CH.  You have to manually overide it and remember to switch it off again.


It's definitely an easy way to do things, it took my plumber a lttle under two days to run the new pipes in for the WBS and make the chnages to the existing system.  Since your WBS is already piped up then I would have thought it could be done in less than a day.  I think a DNV is around £250 new, there are other similar systems and there are posts on this forum about them.

I'll get some more info when I get home tonight and post it on here for you.

Ian.

[Academan]

Thanks for the replies.

Tigger, I would be interested to know what is your pipe layout, specifically how the boiler and the multifuel stove are connected to the Dunsley.

At present with my system, the single flow from the Worcester boiler is split into two (heating and hot water) and these are turned on by two valves (one each for heating and hot water) cotrolled by a Tempus 7 controller. The hot water goes directly to the hot water cylinder. I believe the heating circuit and the multifuel stove circuit are then linked together. The stove circuit has its own pump which is switched on when the temperature reaches a particular level (adjustable). The stove is not connected to the hot water cylinder. The second coil in the hot water cyl. in connected a Navitron solar heating system with TDC3 controller.

Academan

[Tigger]

Hmm, the pipe layout as simplistically as I can explain it.....

The oil boiler has a flow into the Boiler Coil in the Hot Water Cylinder with a Tee going into the Dunsley Neutralizer (DN).  There is a return from the DN via the boiler pump back to the oil boiler

The WBS has a gravity flow and return pipe into the DN with a heat leak radiator off it (in my case the one on the landing outside the airing cupboard).

The Hot Water Cylinder coil has a gravity flow return pipe into the DN

The CH has a flow and return pipe into the DN via the CH pump

The feed and expansion from the F&E tank in the loft are each connected to the DN to serve all pipework

If you go to the Dunsley web site (URL below) there's a very good pipe layout

http://www.dunsleyheat.co.uk/neutralizerlayout2.htm

This one is the wiring layout to go with it

http://www.dunsleyheat.co.uk/layout2.htm

I hope that helps.

If you're anywhere near jct17 of the M4, you're welcome to come and see how it's been done.

Ian.

[dhaslam]

It doesn't seem right at all that the stove back boiler is not connected to the cylinder.     If the cylinder is too far away then a buffer tank somewhere over the boiler should be used  both for safety and to allow stove to reach operating temperature.  The pump would be used to distribute the heat from the buffer tank instead of from the stove.   The Dunsley would allow gravity circulation but would not have enough capacity to absorb overheating if the power goes off.  It is dangerous to have header tanks overheating,  they can melt and spill scalding water into rooms.     

[sleepybubble]

It doesn't seem right at all that the stove back boiler is not connected to the cylinder.     If the cylinder is too far away then a buffer tank somewhere over the boiler should be used  both for safety and to allow stove to reach operating temperature.  The pump would be used to distribute the heat from the buffer tank instead of from the stove.   The Dunsley would allow gravity circulation but would not have enough capacity to absorb overheating if the power goes off.  It is dangerous to have header tanks overheating,  they can melt and spill scalding water into rooms.     

when I reread the OP I notice that the cylinder is on the ground floor... Which indicates that both the oil and Stove are going to be pumped systems. I don't think a Neutralisers is going to be suitable for the OP as they are not too great when being operated with a pumped system, its too easy for the water to be just circulated through the neutraliser.
Sounds like the Flow and return from the Herald are just tee'd into the upstairs heating circuit, with a pump to boost circulation.
I'd reiterate again that the location of the pump on the stove pipework is the most likely cause of the problems irrespective of how much the installation conforms to part J.
Tiggers layout is a fairly typical use of a neutraliser as both the heat sources are gravity cycling to the neutraliser and from the neutraliser to the cylinder with a pumped take off for CH.
When you study the Dunsley diagrams the neutraliser is always located near or just under the cylinder. THe 'c' type being a case example as its designed for the cylinder to sit on top of it. IF academan's cylinder is on the ground floor then a neutraliser would be about as much use a a chocolate teapot.
The OFTEC reccomended method of dealing with multiple heat sources such as oil/WBS is to have two totally seperate heating systems, which is just plain silly TBH.
I think with a few modifications to the existing pipework it would be perfectly feasible to allow the stove to supply both CH and DHW demand, however this may not be desirable dependent upon the size of the property.
Whatever you do, action is imperitive becasue if like your current plumber states you are getting pumpover to the header tank then you will be introducing lots of Oxygen to the system which will dramatically increase corrosion and lead to premature failure of either of the two boilers, as well as increased levels of corrosion in the radiators. If the heating is microbore you will have a fair chance of blockages due to sludge, and the effective lifecycle of any inhibitor added to the system will be greatly shortened too. I don't want to sound all doom and gloom, this could probably be fixed very easily.