[bernie h]

We live in a bungalow and have put in a 14kw stove for the central heating. My system is open vented, I have put the pump in the loft. I have been told that I should have a sink radiator put in in the loft.
We thought that should there be a power failure we would be able to just run off the water and close down the fire?
Can anyone tell me do I need a radiator put in the loft?  if not will my set up be o.k?
Thanks

[lachlanandmarcus]

I'm no expert but from our own experiences and advice I think yes you need the radiator but not sure why it should have to be in the loft....


I'm sure more expert people will confirm or otherwise...

[bernie h]

no idea, we were told to put it in the loft. we are on one level.
I don't understand why we need it there, is it not just the same as going round the radiators in the house?

[Womble]

If your system is all on one level, there will be minimal natural recirculation should the power fail. This means that there's a high likelihood that the system will boil.

The argument goes that the system needs to be inherently safe - i.e. it shuts down without you having to do anything. (Of course the counter-argument goes that with a WBS, you have to be there to feed it in the first place, so why not take action to shut it down yourself should the power fail!).

I think you could run into trouble trying to run the water off though. For a start it's likely to be boiling, then you have to have somewhere safe for it to go, you'd lose all of your treatment chemicals, and would probably also void the warranty on the back boiler by running it dry.

Personally, if there's room in the loft, I'd put a circuit up there with some old second hand radiators, the bigger the better. The rule of thumb is to use 28mm piping for that circuit, and obviously no TRVs. You can isolate them so they're not on all the time by using a zone valve like a V4043B that opens automatically when the power fails (just wire it in parallel with the pump so that it's closed whenever the pump is running).

There are other options, such as having an automatic water flush on high temperature, but TBH I'd only go with that if the simple (cheap) option of the rads in the loft wasn't a goer.

Hope that helps!

[bernie h]

Thank you very much, That has been a great help. Can you tell me what a TRVs is?

Also, our boiler heats the hot water at the same time, it goes through the hot water tank before the radiators and it  has an open vent if it over heats. Will this do, or should we still go for your suggestion.
Kind regards
Bernie

[Womble]

Sorry, TRV is just Thermostatic Radiator Valve:


Where is your hot water tank in relation to the stove?  If it's in the loft, you should get some natural recirculation through the cylinder even if the pump isn't running. However, I doubt it would be enough to rely on in the event of a power cut. The reason I say that is I know our previous system (as it was when we bought this house) used to boil if it switched over onto hot water mode when the range cooker was fired up. Basically when the water cylinder was already warm, there was not enough heat transfer to cool the returning water enough, so it boiled in the back boiler (this was the case even with the pump switched on).

Also, if the cylinder is already hot, there is no driving force to set up the natural recirculation loop in the first place, since it only works due to the densities of hot and cold water being different. You would have a complete system full of relatively hot water, so wouldn't get much recirculation without a pump.

[bernie h]

Thank you again, you have been a great help.  Yes the tank is in the loft.  It looks like I shall go with your suggestions.  So glad that I found this site, I tried on another site and got nothing.

Thank you once again, will get this done, a.s.a.p
 

[bernie h]

Can you tell me where to put it.
I have the pump on the cold water into the boiler, do you mean put the 4039b on the cold water side before or after the pump, or do I put it on the hot water side?

Once again thanks for your help.

[Womble]

Hiya, If your circuit goes through the hot water tank before the rads, then you need to plumb the extra heat leak radiator(s) in in parallel with the hot water tank.

So, if I've understood you correctly, your current system looks something like this:



If that's correct, you need to connect the additional heat leak radiator(s) in parallel so that the hot offtake is between the stove and the hot water cylinder. The return from the heat leak radiator then connects into the existing cold return to the boiler either before or after the pump, depending on what layout works best for you. The key thing is that there should be no restriction in flow to the heat leak, since the driving force for flow is very small.



In this setup, the lines in bold would ideally be 28mm, though if the overall distances are small, you might get away with 22mm?

For the system you've described, it might be worth wiring the heat leak zone valve in with a high temperature pipe thermostat before the hot water cylinder. This would dump heat to stop the cylinder from getting too hot if you got a bit enthusiastic with firing up the stove. That said, if you've not had that problem to date, it might not be worth losing sleep over?

Overall, it's hard to say without seeing the system, and you'd be well advised to get a professional in to have a look if you can find somebody you can trust. At the end of the day, any advice received over the internet (especially from me) is worth exactly what you paid for it, so do be careful  .

Hope that helps!

Womble.

[YoungRasher]

when i was a kid my dad fitted a back boiler to our open fire which ran 7 radiators. the overflow pipe was fitted up the chimney so if the system ever boiled it put the fire out, not sure how legal it would be and i wouldn't recommend it. i remember getting red hot black water splashing on my legs far to often.

[bernie h]

Womble.  You are a super star. Thank you That is the most detailed and helpful answer I could have wished for. You have my system 100% correct. I shall follow your diagrams.
Thank you once again.