Radiators cold at top.. warm at bottom

[kremmen]

Hi,

 

Due to an unexpected problem at home I have had to leave my boat and will not be able to continue to live onboard.

 

I managed to empty the water system and thought I would check my radiators for antifreeze. Shock horror and so I drained as much as I could and then refilled with a strong mix ( about 60% antifreeze ) .

 

When bled and pump turned on and boiler started all I get is hot water at the bottom and cold at the bottom.

 

 

I have tried to bleed any air but only water is coming out of the top of the radiator.

 

It has been suggested that the antifreeze mix is sitting at the bottom of the radiators and plain water at the top .I will try to get the whole system flushed and refilled with a 50/50 mix but cant do that till next week .

 

I was hoping that someone might think of some wheeze I havent thought of to save me trying full flush.

 

Hopefully.

 

Paul Cooke.

[bastion]

shut down all the rads bar one then run heating and try to move any blockage or air lock then work your way through the system one rad at a time.

[GoodGurl]

shut all the rads down ( both valves )start with one rad and open both valves on that rad, then run the pump or heating that should then mix it in that rad, then open the valves on the next rad, closeing the first rad after, repeat for all rads, only having one set of valves open.

[jelunga]

If it is air, then you need ti bleed with heating system OFF. the air will bleed out slowly and you need to enmsure header tank is topped uk all the time so there is a static head to push air out. On our Dberapacher syste , the header tank is only a few inches higher tha. The highest bleed valve but it worns eventhally. So heating off, allow a few minutes for system to settle then bleed lowest bleed valve first.

[ditchcrawler]

Hi,

 

Due to an unexpected problem at home I have had to leave my boat and will not be able to continue to live onboard.

 

I managed to empty the water system and thought I would check my radiators for antifreeze. Shock horror and so I drained as much as I could and then refilled with a strong mix ( about 60% antifreeze ) .

 

When bled and pump turned on and boiler started all I get is hot water at the bottom and cold at the bottom.

 

 

I have tried to bleed any air but only water is coming out of the top of the radiator.

 

It has been suggested that the antifreeze mix is sitting at the bottom of the radiators and plain water at the top .I will try to get the whole system flushed and refilled with a 50/50 mix but cant do that till next week .

 

I was hoping that someone might think of some wheeze I havent thought of to save me trying full flush.

 

Hopefully.

 

Paul Cooke.

Your right is the antifreeze not mixed properly. when I did it (topped up one bottle of water the one antifreeze) I just left the pump running and it eventually sorted its self out. Its a density thing.

[koukouvagia]

Your right is the antifreeze not mixed properly. when I did it (topped up one bottle of water the one antifreeze) I just left the pump running and it eventually sorted its self out. Its a density thing.

 

I agree. However, this might work without your having to drain the whole system. Turn off all the radiators and get the flow and return pipes really hot then open the radiator valves and you may find all is well.

[Justme]

If the pump has a speed selector set it on fast & turn all the rads off bar one. Run pump till that one is hot all over, turn off & repeat for the next rad.

 

 

If the rads are mounted is such a way that they can be lifted off the mounts & the fittings just slackened off enough to allow you to tilt the rad without it leaking so its level/top lower than the bottom or at least at an angle it will help the fluid mix.

[RobinJ]

I managed to empty the water system and thought I would check my radiators for antifreeze. Shock horror and so I drained as much as I could and then refilled with a strong mix ( about 60% antifreeze ) .

Yes, I think the 'strong mix' is the key.

I topped up my towel radiator with neat antifreeze, thinking it would mix, but the antifreeze sank to the bottom and stopped the radiator getting hot at all!

It also seems to depend on the type of antifreeze too, and I think thats because some mix more easily!

Many circulating pumps are also impellor types that don't necessarily develop a great deal of pressure to stir up the system, so if you do have a mechanism (system bypass) to control the flow, than thats the answer, control each section in turn until its fully circulating.

[dor]

As has been said, this is due to the density of the mix. When it happened to me, even shutting off all but one rad at a time still wouldn't clear it. I got it going by using the bleed valve to draw off a litre of water (use ali foil to make a sort of funnel) which went back in the header tank. after a few litres the rad was circulating again.

 

If you consider how small the density difference is between the hot and cold water, which is what drives the circulation inside the rad, you can see how a slug of more concentrated mix will stop the circulation.

[steve hayes]

As has been said, this is due to the density of the mix.

 

I had exactly the same problem, we had had a leak from the Mikuni and the system had been topped with water during the year. Had the Mikuni off the service and on refitting and refilling the system with antifreeze mix the top of the rads stayed cold, no air in rads. Considered the options to try and mix the "water" and went home to think options through.

Came back to the cold boat and turned the heating on and bingo all rads nice and hot.

I assume as the system cooled down an amount of mixing occurred and on start-up the mixing completed.

Anyway result :cheers:

 

Steve

[kremmen]

Thanks all.

I will try the suggestions on here when I return to the boat if it hasn't sorted itself out " in the mix "

 

Paul