Solid fuel stove and disconnected back boiler

[Frank Stacey]

An octogenarian lady who lives near me has recently had full oil-fired central heating installed in her house for free by the local authority. Sounds like a really generous scheme and indeed it is - but...

Before the central heating she had electric heaters and a solid fuel Raeburn stove in the kitchen. This stove had a back boiler to give hot water. The back boiler has been "disconnected" and she was told not to use the stove any more. She recently experienced a 3 day power cut - we are in deepest rural East Lothian - but these things happen often enough. During those 2 or 3 days she had NO HEATING AT ALL. Fortunately the weather was reasonable and she is a very determined lady.

Apologies for the longish introduction. Is it not quite safe to run the stove with a totally empty back boiler system? The metal will get hot but will that matter? There are copper pipes leading up to the attic where, presumably, there is an empty hot water tank. It would be a job of only a few moments to disconnect these - there are very accessible joints just above the stove level. Would such a system be safe to run?

Frank

[Rob Morley]

Would it not make more sense, if the original plumbing is still in place, to reconnect the water even though it goes to a tank that isn't connected to anything else?

[sylva]

Sounds like they have just disconnected the pipes from the back boiler to the hot tank (indirect coil??) and its connection to the expansion pipe and header tank. So if she relit the boiler any remaining water would boil off and the back boiler would overheat and possibly get burnt through. I have heard you can fill them with sand but the worry would be in perforating the back of the firebox and allowing fumes out.

IMO not safe

See above

I don't think so. you need a way of connecting the back boiler into a circuit that can safely dissipate its heat, maybe something on the return side to the oil boiler but I'm no plumber.

AJH

[Christian McArdle]

A Dunsley neutraliser would work, although this might not be compatible with the oil boiler, if it requires sealed pressurised operation. It would have the additional advantage of actually using the solid fuel to heat the water.

An alternative, although probably too late to consider now, is to use a heat bank in these situations. The oil/gas sealed pressurised boiler heats the tank up through the indirect coil in the normal way. The solid fuel range heats through direct water circulation with the heat bank water (no valves or restrictions required) and the DHW is mains water heated off the plate exchanger. A byproduct of this design is to provide mains pressure hot drinking water.

Christian.

[Dave Liquorice]

They didn't do a proper job. IMHO they should have left the Rayburn still functional as a secondary heat source for HW and heating. It should be possible to retro fit a "Dunsley Neutraliser" this allows a oil/gas boiler and solid fuel boiler to co exist on the same system.

Others have pointed out that the boiler will probably burn through or the filling with fine dry sand. No experience, talk to Rayburn?

What sort of system has been installed? Combie (oil combies exist but are rare), presurised or normal open vented? Not sure if a Dunsley Neutraliser can be fitted to anything other than open vented...

[sylva]

Fair enough if they'd done it at the same time, now it will cost a bit to fit and 200 quid to buy. For the small amount of heat lost couldn't the raeburn be sat like a towel rail, then little heat would flow through it and if it was cold in the house the return flow would dissipate the heat?

I was tempted to look at this and decided it was cheaper to put a pump and thermostat in the wood burner circuit but I am open to correction.

AJH

[The Natural Philosopher]

You are supposed to backfill the boiler with sand IIRC but apart from that its OK to use. I think the danger is the boiler side will overheat and melt, and the sand cools it and transfers the heat away.

I simply left my Highlander stove water pipes unconnected, and have used it a few times since.

No probs to date.

[Pete C]

Hi,

Get the council to reinstate the back boiler as was, and make the new system run in parallel with the old.

cheers, Pete.

[Neal Jones]

I undersatnd that there are firebricks that can be used to replace the boiler, it's not a technically difficult job, but if the rayburn is 'well embedded' this may not be an option. I have a single panel radiator and a pump on my rayburn (vented to a header tank in the room above), keeps the kitchen toasty.

I looked into a dunsley neutraliser, but the cost and PITA factors were too much for what is, after all, a secondary heat source.

NUJ

[Dave Liquorice]

Trouble is you don't want to pump the primary without Dunsley Neutraliser as the Rayburn really needs to be on gravity. If you pump the primary without a Neutraliser you'll circulate water through the Rayburn which will shift some of that heat up it's flue. And with oil at silly prices you don't want to waste it...

So when the power goes off you have to shut down your woodburner to stop it's boiler boiling or worse, exploding. Seems a bit silly...

[sylva]

How so if the raeburn is not in use, isn't the flue dependant on a hot firebox to circulate air up through it? If it's solid fuel the air inlet could be kept closed, with a properly sealed system the heat transfer from the back boiler to an air path up the flue would be negligible.

You just said it normally works as a gravity system, with power off worst case is the water in the header tank boils, at least you have some local heat for comfort. I assumed the OP's boiler was solid fuel.

In the event in my case I just left the gas central heating in place and replaced the boiler (potterton suprima :-(), I have a jotul in my office and a 10kW(t) pellet stove in the living room and if we ever have a lengthy power cut will attempt to run the heating with a petrol generator.

AJH

[Dani]

replying to The Natural Philosopher, Dani wrote: Did you fill the boiler with sand ?

[Graeme]

Well, that was 16 years ago, but yes, when my Stanley stove/boiler was disconnected from the water, I filled the water tank with dry sand, and it was fine. The stove part was used all year, only closing down briefly in the summer for annual cleaning.

[The Natural Philosopher]

No.

18 years later, its fine