Back boiler and diesel heater together

[Garry arnold]

Hi all I have a diesel heater eberspacher fitted in engine bay and would like to connect the back boiler to the system it has a expansion tank at the back should I fit a 12 volt pump to the rear and put a bleed valve on the stove outlet would the expansion tank be ok at the rear the back boiler stove is fitted at the front Narrowboat is 46 ft long with 4 radiators any help appreciated many thanks 

[BEngo]

You can fit two sources of heat to one installation but it is complex:

The water needs to circulate the same way round regardless of which heat source is in use. This is hard to do if the heat sources are at opposite ends of the system.

You need to ensure that only one heat source is going at any one time.

If there is a pump for one source and the other is gravity circulated the pump, when off, must not impede the gravity circulation.

If there is s calorifier for hot water things will be even more complicated.

Any solid fuel system that depends entirely on a pump for circulation is risky, if not dangerous.  The pump will at some point fail and the system will then boil.

 

The expansion tank can be anywhere in the system.  Ideally the bottom is connected to the return pipe and the top  to the flow pipe as an open vent.

You probably do not need  a vent at the back boiler if the flow pipe rises as it should.

What is the back boiler connected to now?

 

N

[Garry arnold]

We have connected it to the end of the radiator circuit the pipes have to go down to the floor to go round the boat I am going to fit a couple of pumps so I have a back up pump we have only just fitted the back boiler 

Both systems will have pumps and I can wire it up so one pump works and the other one I can be switched on as a safety thing if one packs up

[Alan de Enfield]

50 minutes ago, Garry arnold said:

Both systems will have pumps and I can wire it up so one pump works and the other one I can be switched on as a safety thing if one packs up

The problem with pumps is that you may not realise that one has 'packed up', it only takes minutes of no circulation for the water in the back boiler to boil. turn to steam  and 'explode' your system.

 

Pumps are dangerous and should not be used.

Design your system to be gravity / thermo-syphon driven.

[ditchcrawler]

I go alone with Alan on this, pumped back boilers, especially with pipe states and cold shock to the boiler etc.

On the question of two heat sources we had this on Waterwitch with a back boiler at the bows and an Eberspacher in the engine bay. The back boiler had a pump and pipe stat which pumped the water in the same direction as the Eberspacher, it actually worked quite well, just one pump but the one header tank that would throw a hissy fit if the fire was going well until that side of things started working properly (which they never do) but with the Eberspacher it worked fine.

[Garry arnold]

Was just going to just have the pump running for the time the fire is on so hopefully no cold shock and I understand the problems with pumps not working so will put an override on the eberspacher pump so if I ever have a problem I can turn that pump on separately from the eberspacher heater just till I can put fire out 

[Alan de Enfield]

8 minutes ago, Garry arnold said:

Was just going to just have the pump running for the time the fire is on so hopefully no cold shock and I understand the problems with pumps not working so will put an override on the eberspacher pump so if I ever have a problem I can turn that pump on separately from the eberspacher heater just till I can put fire out 

The point was more to do with "how will you notice the pump has failed " (within the limited time before it goes 'bang')

[Oddjob]

On 03/12/2020 at 09:43, Alan de Enfield said:

The problem with pumps is that you may not realise that one has 'packed up', it only takes minutes of no circulation for the water in the back boiler to boil. turn to steam  and 'explode' your system.

 

Pumps are dangerous and should not be used.

Design your system to be gravity / thermo-syphon driven.

What happens as long as the system is not a sealed pressure system is if pump fails water in the back boiler turned to steam and the expansion pushes the water in the pipe back into the header tank which now over flows and dumps the water on the floor/bilge then if you have plastic pipes near the fire they melt. This I know as just before I brought my boat the broker got the fire going to show a buyer but did not turn on the pump and above took place. When I got the boat I found water in the bilge and when I asked the marina based engineer he told me the story. Cleaned out the water and no more issues. I plan to move the pump to a better place as access is under the bed stowage so I have to empty the stowage to get to the pump. I plan to replace the pump before next winter as it’s a new pump in September 2019 as it was leaking will replace as prevention is better than cure in this case as it’s running 24x7 now. It was only £70 so not to much for peace of mind

[Garry arnold]

Hi it’s not a sealed system it has a vented expansion tank so shouldn’t be to bad it’s all copper pipes by the fire so I am sure moving the pump will cure my problem

[ditchcrawler]

Providing the steam can get through the pipes fast enough from the boiler and open to vent