Back Boiler/How Water Woes.....

[junior]

From my explanation below, can anyone offer any thoughts on what is going on with my hot water system?

 

Since owning the boat I've always had hot water issues. The pipe from the top of the back boiler gets hot all the way through to where it goes into the calorifier, then the pipe that comes out is cold. In between the back boiler and calorifier is a radiator, this is hot at the top and freezing at the bottom. The first time I bled the system I got a little air then anti-freeze but from then on regular bleeding only gets blue liquid. The water has never got above luke-warm. I posted about this a few months back and it was diagnosed by a few as an air lock, but with no solutions suggested I've just come to accept that's how it is. I cruise regularly and get hot water off my engine as well so it's never been to much of a problem. Until now as I'm staying put for xmas and new year.

 

Yesterday I decided to remove the fire brick that halves the size of the grate in my SFS. The way it was positioned also meant that half of the back boiler was covered by the brick therefore the flames only get to top half of the back boiler and the bottom half of it is hidden behind the fire brick with a small void in between. In crazy 'junior logic', I thought this might be the reason only the top half of my hot water system was getting warm.

 

After about an hour of the stove being lit I heard the sound of rushing waster coming from my engine room. I ran down there thinking the boat had sprung a leak, only to find the open topped expansion tank on the wall spewing anti-freeze all over the floor. I scooped some out to bring the level down and then just sat and watched while it bubbled like a witches cauldron. It carried on like this for ages.

 

After a while I thought I'd try bleeding the radiator. I got air/steam for about 10 mins at which point I got bored and closed the valve. This seemed to do the trick and stopped the expansion tank bubbling for a while. Periodically I kept going back and bleeding some more air/steam from the radiator, but at no time did I get liquid.

 

A while later the expansion tank started bubbling uncontrollably filling the engine room and back cabin with anti-freeze smelling fumes. It even set off the CO Alarm in the back cabin.

 

I decided I would have to persevere with getting the air out of the system and went back to bleeding the radiator. I opened the valve fully and had high pressure air/steam coming out. I left it open and vacated the boat as I was starting to feel ill from the fumes. After an HOUR it was still steam/air coming out and no sigh of blue liquid like I used to get when bleeding the rad. I gave up, ventilated the boat and went to bed to the sound of the expansion tank bubbling/gurgling away.

 

This morning I've got up and instead of the radiator being hot at the top like it used to be, it is freezing cold. The pipe coming along the top from the SFS to the calorifier is still hot though. I also have freezing cold water whereas before it was luke warm.

 

Removing this fire brick seems to have done the opposite to what I had hoped. Any ideas???

[jelunga]

From my explanation below, can anyone offer any thoughts on what is going on with my hot water system?

 

Since owning the boat I've always had hot water issues. The pipe from the top of the back boiler gets hot all the way through to where it goes into the calorifier, then the pipe that comes out is cold. In between the back boiler and calorifier is a radiator, this is hot at the top and freezing at the bottom. The first time I bled the system I got a little air then anti-freeze but from then on regular bleeding only gets blue liquid. The water has never got above luke-warm. I posted about this a few months back and it was diagnosed by a few as an air lock, but with no solutions suggested I've just come to accept that's how it is. I cruise regularly and get hot water off my engine as well so it's never been to much of a problem. Until now as I'm staying put for xmas and new year.

 

Yesterday I decided to remove the fire brick that halves the size of the grate in my SFS. The way it was positioned also meant that half of the back boiler was covered by the brick therefore the flames only get to top half of the back boiler and the bottom half of it is hidden behind the fire brick with a small void in between. In crazy 'junior logic', I thought this might be the reason only the top half of my hot water system was getting warm.

 

After about an hour of the stove being lit I heard the sound of rushing waster coming from my engine room. I ran down there thinking the boat had sprung a leak, only to find the open topped expansion tank on the wall spewing anti-freeze all over the floor. I scooped some out to bring the level down and then just sat and watched while it bubbled like a witches cauldron. It carried on like this for ages.

 

After a while I thought I'd try bleeding the radiator. I got air/steam for about 10 mins at which point I got bored and closed the valve. This seemed to do the trick and stopped the expansion tank bubbling for a while. Periodically I kept going back and bleeding some more air/steam from the radiator, but at no time did I get liquid.

 

A while later the expansion tank started bubbling uncontrollably filling the engine room and back cabin with anti-freeze smelling fumes. It even set off the CO Alarm in the back cabin.

 

I decided I would have to persevere with getting the air out of the system and went back to bleeding the radiator. I opened the valve fully and had high pressure air/steam coming out. I left it open and vacated the boat as I was starting to feel ill from the fumes. After an HOUR it was still steam/air coming out and no sigh of blue liquid like I used to get when bleeding the rad. I gave up, ventilated the boat and went to bed to the sound of the expansion tank bubbling/gurgling away.

 

This morning I've got up and instead of the radiator being hot at the top like it used to be, it is freezing cold. The pipe coming along the top from the SFS to the calorifier is still hot though. I also have freezing cold water whereas before it was luke warm.

 

Removing this fire brick seems to have done the opposite to what I had hoped. Any ideas???

[PaulJ]

You certainly seem to have an airlock causing your circulation problems. I would hazard a guess that at the very least you really need a vent fitting probably somewhere near the boiler.

[jelunga]

You have now boiled the water in the system by too much heat into back boiler. Created steam and even more air in the system. List most of your water.

My advice is to drop fire asap, let it cool and replace fire brick and hope you have not distorted the back boiler by overheating it!

[Pete & Helen]

You haven't said if your on a gravity or pumped system but I am assuming from the description that its gravity.

 

The cause of boiling is down to low or no water flow in the system. This can be a blockage (sludge in the system), or where the pipe work hasn't a large enough bore (normally 28mm for gravity systems). Also the way the pipe is routed can effect the flow, the hot pipe out of the boiler should flow upwards to the end of the system which is normally the hot water tank then down hill back to the boiler, bends should be gradual. An air lock can happen if there is any rise then dip in the pipe work. a bleed valve at the highest level in the pipe work should clear any air.

 

For the radiators. turn the valves off, the bleed the pipe work. then open the bottom (cold end) valve and bleed valve. then do the same with the second radiator. you should now have a clear system and can turn the top valves on.

 

Do all the above with the fire out. Hopefully this should solve your problem

[BEngo]

As Jelunga says.

 

Refill the system with water only and check for leaks with the system warm. If OK then drain and refill with 50% antifreeze, otherwise you may just waste a fill of antifreeze.

 

The system seems to be working OK , but can't circulate the water fast enough to heat the water in the calorifier. It is not uncommon for the radiators to only get hot at the top in this case- the water is meant to cool down as it goes through the rad, but in your case it is cooling off completely. The cal is similar. The top pipe should be a lot hotter than the bottom one, when the tap water is cold. As the tap water warms up less heat can get out of the heating water and into the tap water so the bottom pipe will warm up. Because you have very slow circulation the water will take ages to warm up.

 

What size are the pipes? Really for gravity circulation they will need to be at least 22mm and ideally bigger (28mm)if you want to run the boiler fairly fast. the pipes to the rads can be 15mm but must be a short as possible and ideally enter at diagonally opposite corners of the rad.

 

 

Things you can do without completely re-designing the system:

 

Live with it :-) Or:

 

Fit a pump in the bottom pipe which pushes water through the boiler. EG: www.mackengineering.co.uk/products/CM30P7%252d1-JOHNSON-CIRCULATING-PUMP-12v-MAG-DRIVE.html

 

There are much cheaper ones about if you Google around solar water heating. This will enable you to run a bigger/hotter fire without boiling the water and should get both the rad and the cal hot. You can control the pump with a cylinder stat on the top pipe, near the boiler, so that the pump only runs when the pipe is hot enough. Put a on/off switch in parallel so you can run the pump occasionally in summer just to keep it unseized.

 

Check that any valves in the pipe run are fully open- the lower valve on the rad may not be as this is used to balance the flow through the rad and the cal so that as much water goes through the calorifier as through the rad. If it's not fully open then count the turns and part-turns needed to open it.

 

Check that there is a good rise in the top pipe and a fall in the bottom pipe- filling the bow water tank usually helps here.

 

 

N

[nicknorman]

Yes by removing the fire bricks you have increased the heat to the back boiler without sorting out the circulation issues, thus boiling off much of the coolant. Obviously you need to replace the firebricks at least until the circulation is improved. Do you know if this system ever worked properly? ie it could be a fundamental design problem. I believe it is quite difficult to get good gravity circulation through a calorifier, maybe you should consider installing a low power circulating pump - this would probably fix all the problems, at the expense of a little power drain from your batteries.

[junior]

You haven't said if your on a gravity or pumped system but I am assuming from the description that its gravity.

 

The cause of boiling is down to low or no water flow in the system. This can be a blockage (sludge in the system), or where the pipe work hasn't a large enough bore (normally 28mm for gravity systems). Also the way the pipe is routed can effect the flow, the hot pipe out of the boiler should flow upwards to the end of the system which is normally the hot water tank then down hill back to the boiler, bends should be gradual. An air lock can happen if there is any rise then dip in the pipe work. a bleed valve at the highest level in the pipe work should clear any air.

 

For the radiators. turn the valves off, the bleed the pipe work. then open the bottom (cold end) valve and bleed valve. then do the same with the second radiator. you should now have a clear system and can turn the top valves on.

 

Do all the above with the fire out. Hopefully this should solve your problem

The system is gravity fed as far as I'm aware. I only have one radiator and it only has one on/off valve at the bottom. At the top is the bleed valve. So I'm not sure that I can isolate the rad and then bleed the pipework.

 

When I get home in a little while I will attempt to take some photos and upload them on here.

As Jelunga says.

 

Refill the system with water only and check for leaks with the system warm. If OK then drain and refill with 50% antifreeze,

 

 

N

How do I refil the system? The header tank still has anti-freeze mix in it so I'm guessing it hasn't boiled dry.

[PaulJ]

Is the radiator below the pipe that comes from the top of back boiler though?

[junior]

Yes by removing the fire bricks you have increased the heat to the back boiler without sorting out the circulation issues, thus boiling off much of the coolant. Obviously you need to replace the firebricks at least until the circulation is improved. Do you know if this system ever worked properly? ie it could be a fundamental design problem. I believe it is quite difficult to get good gravity circulation through a calorifier, maybe you should consider installing a low power circulating pump - this would probably fix all the problems, at the expense of a little power drain from your batteries.

 

No I don't know for sure if it ever worked properly, but knowing who did the cabin conversion I'd like to think it was all done properly in the first place.

 

Most problems I seem to be having with the boat seem to be related to the fact it sat in a marina for years not being used and now I'm asking everything to be used 24/7 it's protesting!

 

I'm hoping to get enough ideas off here for things I can try myself first before needing to spend money. Having had both fuel pumps go bang the week before xmas I don't have any money available for a while to fix this!

Is the radiator below the pipe that comes from the top of back boiler though?

Yes it is.

 

Pipe comes out of top of SFS and runs at gunwhale level through the boat to the calorifier. Just before the calorifier there is a t-junction going down to the radiator.

Coming out of the calorifier it goes down to skirting board level and goes back through the boat to the bottom of the SFS. Just after it comes out of the calorifier is another t-junction going up into the bottom of the radiator.

 

So its like one big circle, with the Rad making a smaller circle within the big circle. The top half of the big circle is hot, the bottom half cold.

[MtB]

1) The water in the back boiler is boiling because there is too little circulation to carry away the heat being absorbed by the water in it.

 

2) This is probably a system design problem and the brick in the stove was put there to address the symptom rather than the cause.

 

3) If there is no pump, then it is a natural convection system and pipe diameters, pipe gradients and type of radiator isloator valve become critical.

 

4) If convection, one of the rad connections needs to be at the top of the rad and rise verically UP to and connect into the flow pipe.

 

5) A heat load on a natrural convection system MUST be higher than the heat source, i.e. the back boiler or it will not work. The best a convection system will ever do is make the heat load the same temp as the back boiler, height for height. This means a heat load will never get properly hot below the height of the base of the back boiler.

 

6) If the stove is at the front of the boat and the heat load towards the back (as usual) the calorifier will need to be surprising high up to work at all.

 

Is your calorifier horizontal or vertical format?

 

 

MtB

[junior]

1) The water in the back boiler is boiling because there is too little circulation to carry away the heat being absorbed by the water in it.

 

2) This is probably a system design problem and the brick in the stove was put there to address the symptom rather than the cause.

 

3) If there is no pump, then it is a natural convection system and pipe diameters, pipe gradients and type of radiator isloator valve become critical.

 

4) If convection, one of the rad connections needs to be at the top of the rad and rise verically UP to and connect into the flow pipe.

 

5) A heat load on a natrural convection system MUST be higher than the heat source, i.e. the back boiler or it will not work. The best a convection system will ever do is make the heat load the same temp as the back boiler, height for height. This means a heat load will never get properly hot below the height of the base of the back boiler.

 

6) If the stove is at the front of the boat and the heat load towards the back (as usual) the calorifier will need to be surprising high up to work at all.

 

Is your calorifier horizontal or vertical format?

 

 

MtB

It's vertical in the bathroom next to the radiator.

 

What is a 'heat load'?

 

I'm going to take a load of photos and attempt to upload them on here.

[BEngo]

You re-fill the system by opening the bleed valve on the radiator and keeping the expansion tank topped up until water comes out of the rad bleed valve. Then shut it off. That will mostly fill it, but may not completely fill the top pipe ( because I expect the rad bleed valve is below the top pipe).

 

 

The reason you can see liquid in the tank is because the system boiled and turned a lot of coolant to steam. When it eventually cooled down the steam turned back to water, but quite a lot will have been lost into the engine hole and the top pipe is now quite probably empty. To get the system to start circulating again you HAVE to get all the air out of the top pipe.

 

Do you have a diagram or piccys of how the pipes run and what sort of fittings are used -soldered or compression? If you do we can comment on where the air is likely to be, and how you might get it out.

 

N

[MtB]

It's vertical in the bathroom next to the radiator.

Good, sort of. Horizontal ones don't have a prayer of working on a cenvection system, so had yours been horizontal, this would have been the design error.

 

 

 

What is a 'heat load'?

Anything you want heated up by the back boiler. Radiator, towel rail, hot water cylinder. Underfloor heating circuit...

 

 

MtB

You re-fill the system by opening the bleed valve on the radiator and keeping the expansion tank topped up until water comes out of the rad bleed valve. Then shut it off. That will mostly fill it, but may not completely fill the top pipe ( because I expect the rad bleed valve is below the top pipe).

You shouldn't need to do this on a well designed natural convection system.

 

The top rad connection will allow radiator and pipework air to escape via the flow pipe to the open vent. The cold fill will connect into the bottom of the system and fill it from the bottom upwards.

 

MtB

[junior]

You re-fill the system by opening the bleed valve on the radiator and keeping the expansion tank topped up until water comes out of the rad bleed valve. Then shut it off. That will mostly fill it, but may not completely fill the top pipe ( because I expect the rad bleed valve is below the top pipe).

 

 

The reason you can see liquid in the tank is because the system boiled and turned a lot of coolant to steam. When it eventually cooled down the steam turned back to water, but quite a lot will have been lost into the engine hole and the top pipe is now quite probably empty. To get the system to start circulating again you HAVE to get all the air out of the top pipe.

 

Do you have a diagram or piccys of how the pipes run and what sort of fittings are used -soldered or compression? If you do we can comment on where the air is likely to be, and how you might get it out.

 

N

 

That's what I was hoping to do last night when I left the bleed valve open. The level dropped a little bit in the header tank but not much during the hour I had the bleed valve open for.

 

The fire is still lit, so the system hasn't cooled down yet.

 

I'll take some photos but I've never been able to work out how to get them on here properly.

[BEngo]

SNIP

 

MtB

 

 

You shouldn't need to do this on a well designed natural convection system.

 

The top rad connection will allow radiator and pipework air to escape via the flow pipe to the open vent. The cold fill will connect into the bottom of the system and fill it from the bottom upwards.

 

MtB

I agree entirely, but this system is evidently not "a well designed natural convection system" or Junior would not need to be posting as he is.

 

N

[junior]

This is at the top of the pipe that comes out of the top of the back boiler. I've tried a screwdriver in it but it won't budge. I think it's also the highest point in the system.

 

http://farm4.staticflickr.com/3673/11732910866_a55c131240_b.jpg[/iig]

 

This is the back of the SFS

 

http://farm8.staticflickr.com/7367/11732136215_bc1dda2d4f_b.jpg

 

This is next inline (to the left is the SFS and to the right is calorifier)

 

http://farm4.staticflickr.com/3737/11732520314_e66a0ce62c_b.jpg

 

 

Top of rad

 

http://farm6.staticflickr.com/5537/11732851366_6267f5c22b_b.jpg

 

Rad in full

 

http://farm3.staticflickr.com/2845/11732342003_c5471b9bd4_b.jpg

 

Bottom of rad

 

http://farm8.staticflickr.com/7411/11732063615_8bea2fbe8e_b.jpg

 

 

Bleed valve

 

http://farm4.staticflickr.com/3787/11732808566_d240ca74c5_b.jpg

 

 

Bottom pipe. To the left is the return to the SFS and to the right is the bottom of calorifier. Don't know what that valve in pic does

 

http://farm6.staticflickr.com/5479/11732797366_408917bc11_b.jpg

 

 

Don't know what this is but it seems to be inline the top pipe between rad and calorifier

 

http://farm4.staticflickr.com/3805/11732781046_3244571ccc_b.jpg

 

Calorifier

 

http://farm4.staticflickr.com/3695/11732258413_aa39ebe619_b.jpg

Edited January 3, 2014 by junior

[matty40s]

try something at 90 degrees to it with a flat edge that will fit the slot like the back of a knife. If it's been in there 20 years, it may take some getting out.

[junior]

try something at 90 degrees to it with a flat edge that will fit the slot like the back of a knife. If it's been in there 20 years, it may take some getting out.

Dumb question.....why do I need to undo it?

 

Rest of pics added to my post.

[matty40s]

Dumb question.....why do I need to undo it?

 

Rest of pics added to my post.

well I thought trying a screwdriver was you trying to undo it.......

 

If it is the highest point, there may be an airlock there. If you manage to loosen it slightly, you will either hear steam, or see liquid.....answering the airlock question.

[PaulJ]

Anything that is a tight fit in the slot! Huge screwdriver, coin in a pair of grips etc. Pair of grips if all else fails and the head gets chewed up ...

Feeling optimistic for you-refill and bleed with vent in picture and think you will be sorted!

[junior]

well I thought trying a screwdriver was you trying to undo it.......

 

If it is the highest point, there may be an airlock there. If you manage to loosen it slightly, you will either hear steam, or see liquid.....answering the airlock question.

Yep gotcha, I thought thats why but was just checking.

Anything that is a tight fit in the slot! Huge screwdriver, coin in a pair of grips etc. Pair of grips if all else fails and the head gets chewed up ...

Feeling optimistic for you-refill and bleed with vent in picture and think you will be sorted!

So are you saying you think I just need to keep bleeding it and make sure the header tank has liquid in to replace?

[matty40s]

http://farm4.staticflickr.com/3805/11732781046_3244571ccc_b.jpg

 

have you tried bleeding it using this bit??

[PaulJ]

Yep gotcha, I thought thats why but was just checking.

 

So are you saying you think I just need to keep bleeding it and make sure the header tank has liquid in to replace?

Yep. May my optimism be passed to you...

And that bit I didnt see that Mattys just pointed out lol.

Edited January 3, 2014 by PaulJ

[junior]

http://farm4.staticflickr.com/3805/11732781046_3244571ccc_b.jpg

 

 

 

have you tried bleeding it using this bit??

No, I only found that today when taking photos. Is it the vent that someone suggested I have fitted?

 

Do I twist the knobbly screw bit at the very top or the spanner shaped bit underneath?