Back boiler - will it cause a prob if I turn the pump off while the fire is going?

[Rocinante]

Hi, I have been told that if I have a fire when the pump for my back boiler is not working. I think they said the water could boil over & cause a problem. Is this true?

 

The pump uses a lot of power and I would like to switch it off while we are in front of the fire, only turning it on before we go to bed in the other room, but I do not want to damage my pipes.

[Chris-B]

Hi, I have been told that if I have a fire when the pump for my back boiler is not working. I think they said the water could boil over & cause a problem. Is this true?

 

The pump uses a lot of power and I would like to switch it off while we are in front of the fire, only turning it on before we go to bed in the other room, but I do not want to damage my pipes.

 

Yes this could well result in damage.. I would suggest a low amperage 12v ch pump

The two propriety names dont spring to mind at the moment but somebody else with a better memory than me will be along soon ( jabsco make one of them )

Chris

 

 

 

 

[Keeping Up]

It depends on how hot you have your fire, but basically yes it can happen. The water in the boiler can indeed boil, with consequences ranging from (best case) loud gurgling noises through (likely case) jets of water or steam from the overflow to (worst case) a plumbing joint being forced apart by the pressure.

 

This isn't just theoretical; on our previous boat the heating system was rather unusual and #1 & #2 of these were regular occurrences (but thankfully not #3).

 

Keep the pump going.

[The Bagdad Boatman (waits)]

The alternative is to ensure that a gravity method will work hot water being lighter than cold if your pipes are big enough and are in the right position.

[rjasmith]

Yes this could well result in damage.. I would suggest a low amperage 12v ch pump

The two propriety names dont spring to mind at the moment but somebody else with a better memory than me will be along soon ( jabsco make one of them )

Chris

 

Bolin is probably the other one. Really quiet running and very low power consumption (150mA from memory).

 

However very expensive and supposed to be not that long lived (shaft seal wears out).

 

I have seen some pumps on eBay that are very cheap, use sealed armature/impeller ie no shaft seal. These are around £30 but are a bit more power consuming than the Bolin. Must try one out one day.

 

Richard

[Keeping Up]

I found that the early Johnson pumps were very short-lived but the modern ones, with the magnetic drive, are fairly quiet and long-lived. They too take more power than the Bolin.

[jonathanA]

I've not used these personally but they were recommended in another thread on here and I thought I'd make a note for a future heating project...

 

since they are designed for solar they should be just fine for boats and only take 0.5 amp or so

 

http://www.solarproject.co.uk/page2.html

 

edited to add: there's been a recent case near me were a stove in a house blew up (literally), the back boiler was fitted but as the owner hadn't got around plumbing it in he capped it off and the thing literally exploded sending shrapnel flying - luckily no one was home at the time so a bit of care is needed with back boilers as there is no 'off' switch

Edited January 20, 2012 by jonathanA

[rjasmith]

I've not used these personally but they were recommended in another thread on here and I thought I'd make a note for a future heating project...

 

since they are designed for solar they should be just fine for boats and only take 0.5 amp or so

 

http://www.solarproject.co.uk/page2.html

 

Yes that's the one I've seen on eBay.

 

Richard

[wandering snail]

I've not used these personally but they were recommended in another thread on here and I thought I'd make a note for a future heating project...

 

since they are designed for solar they should be just fine for boats and only take 0.5 amp or so

 

http://www.solarproject.co.uk/page2.html

 

edited to add: there's been a recent case near me were a stove in a house blew up (literally), the back boiler was fitted but as the owner hadn't got around plumbing it in he capped it off and the thing literally exploded sending shrapnel flying - luckily no one was home at the time so a bit of care is needed with back boilers as there is no 'off' switch

Thanks for this link,could be useful next time the Bolin plays up again.

[Rocinante]

Thank you all. Some great tips. The solar pumps do look like great value. I will keep the pump on, though I am tempted to disconnect the system & just go with the simplicity of an eco fan...something for the future perhaps.

[nicknorman]

Thank you all. Some great tips. The solar pumps do look like great value. I will keep the pump on, though I am tempted to disconnect the system & just go with the simplicity of an eco fan...something for the future perhaps.

Please be careful to fully drain the system of water if you disconnect it. As mentioned, back boilers can violently explode if there is water in them not circulating - the water boils and gets pushed away from the boiler by steam ( water vapour for the pedants), allowing the boiler to heat up well beyond boiling point. That is not a problem until a small amount of water finds its way back into the boiler since there is no longer any steam pressure keeping it away. The water hits the very hot boiler metal and instantly boils with sudden massive pressure build up. In the confines of a back boiler this causes an explosion and lots of shrapnel!

[ditchcrawler]

I found that the early Johnson pumps were very short-lived but the modern ones, with the magnetic drive, are fairly quiet and long-lived. They too take more power than the Bolin.

I have one of them and find it a little noisy

 

The alternative is to ensure that a gravity method will work hot water being lighter than cold if your pipes are big enough and are in the right position.

That would probably involve re-plumbing the whole heating system

[blackrose]

Thank you all. Some great tips. The solar pumps do look like great value. I will keep the pump on, though I am tempted to disconnect the system & just go with the simplicity of an eco fan...something for the future perhaps.

 

As far as I am aware if there is a backboiler in the stove then it has to be filled with (circulating) water. I may be wrong but I don't think you can simply empty the system, disconnect the pipes and then light the fire - it's the equivalent of putting an empty kettle on the hob.

 

Why not just buy a new pump and install it between 2 isolation valves so that if it ever goes wrong in future then you don't even need to drain the system to change it?

Edited January 21, 2012 by blackrose

[Chertsey]

As far as I am aware if there is a backboiler in the stove then it has to be filled with (circulating) water. I may be wrong but I don't think you can simply empty the system, disconnect the pipes and then light the fire - it's the equivalent of putting an empty kettle on the hob.

 

 

Well you can, providing you don't want to use it again. But it will probably damage the backboiler.

[MtB]

As far as I am aware if there is a backboiler in the stove then it has to be filled with (circulating) water. I may be wrong but I don't think you can simply empty the system, disconnect the pipes and then light the fire - it's the equivalent of putting an empty kettle on the hob.

 

Yes you can. The important thing is NOT to cap off the pipe connections, thus preventing any pressure developing in the back boiler chamber.

 

It may well crack as Chertsey says, but it will remain safe from explosion. Whether it leaks carbon monoxide out into the living space when cracked is another issue. Quite a possibility in my view.