Gravity fed radiators and alarming noises??

[wobbly ollie]

We have a Morso Squirrel with back boiler from which we are running 2 radiators. Both rads get nice and warm once the fire has been running for an hour or so. The top pipe (25 mm approx) that runs the length of the boat to the rads gets really hot whereas the lower pipe (return?) stays cool which I understand is all correct? The header tank content and pipes also remain cold. Our problem is an intermittent banging that comes from the top pipe every 15 minutes or so. Its quite alarming...almost like someone is hitting the hull with the hammer! 3 or 4 bangs then it stops. Most odd. My first though was to bleed the rads of any air however having loosened the bleed screws, no air was evident as both produced a ready flow of hot water into the waiting tea towel... Any though welcome and appreciated ??

[Tony Brooks]

My old Parkray used to do that at home. I think it was limescale in the boiler allowing localised boiling under the limescale. What happens if you turn the burn rate down or set a smaller fire?

 

You could try some boiler silencer fluid in the header tank if its still available or next spring even descale the boiler but lets see what others think.

[NB Lola]

I would have thought something like fernox would do the job. There are other providers, try a google using Tony's phrase.

[Bee]

I knew a system that did that, it was struggling to circulate by gravity and from time to time would reverse, i.e. hot water would shoot up the return pipe, it was only for a second or two then it would correct itself, I would just check the pipes are hot on top/ cool below immediately after or during its little upsets. It was cured by making the header tank pipe bigger, relocating it precisely at the top of the circuit and bunging a few more bricks under the floor at the front.

[Neil Smith]

Surley the return pipe should get hot if the gravity is working properly, the noise is whats known as pipe hammer and could be the water boiling in the flow pipe as it isnt returning to spread the heat.

 

Neil

[MtB]

I too am inclined to suspect the banging noise described is the water in the back boiler boiling.

 

Fit a pump to assist circulation and all the noises will probably vanish.

 

Unfortunately a load of other problems result from fitting a pump. Most to do with ensuring a permanent power supply...

[wobbly ollie]

Thanks everyone. I think I'll start with Fernox to see if that clears the pipes. It does seem worse when the fire is on high burn so i think the general assesment of water boiling in the pipes is likely. I'll keep you updated.

[MtB]

Thanks everyone. I think I'll start with Fernox to see if that clears the pipes. It does seem worse when the fire is on high burn so i think the general assesment of water boiling in the pipes is likely. I'll keep you updated.

 

 

It's not boiling 'in the pipes'. Its boiling in the heat exchanger inside the stove.

[Giant]

Our system is pump driven but we will get the same banging if the fire heats up very quickly and/or the thermostat controlling the pump is set too high.

 

Either fit a pump or find some other way to improve the circulation and it should stop.

[MtB]

Our system is pump driven but we will get the same banging if the fire heats up very quickly and/or the thermostat controlling the pump is set too high.

 

Either fit a pump or find some other way to improve the circulation and it should stop.

 

 

If the pump isn't running because the thermostat has turned it OFF, what do you expect?!

[Giant]

If the pump isn't running because the thermostat has turned it OFF, what do you expect?!

 

For the pump to come back on when the thermostat is back up to its trigger temperature of course!

 

You say this as if it would be obviously stupid to have the thermostat set too high, but in our case at least, it's hard to find the best setting to leave it at. The pipes from the back boiler run through a wall to get to the cupboard with the thermostat & the rest of the plumbing, so it's a short distance removed from the back boiler itself. As such there's a delay between the boiler getting hot and the thermostat getting hot.

 

If the thermostat is set to what might seem a reasonable temperature, we can still sometimes get some brief banging before the pump kicks in, if the stove heats up quickly enough. If set low enough to completely prevent this in all cases, the boiler doesn't get the water hot enough to be useful.

 

Yes it's silly and we should move the thermostat closer to the boiler, but it's a boat so there's a zillion more pressing jobs to do.

[MtB]

I'd say having a thermomstat at all controlling a pump distributing the heat from an uncontrolled heat source like a solid fuel stove, is daft.

 

The pump needs to run all the time the stove is alight.

[David Mack]

I'd say having a thermomstat at all controlling a pump distributing the heat from an uncontrolled heat source like a solid fuel stove, is daft.

 

The pump needs to run all the time the stove is alight.

 

Agreed. The amount of heat put out will be pretty much the same whether the pump is running or not, so the only saving is in the electricity used by the pump. If you must fit a thermostat, then a pipe thermostat fitted close to the boiler outlet will set the pump running whenever the stove is lit.

[peterboat]

My system is controlled by a pipe stat works fine. I remember from years ago that some systems had two pipe stats, one to start the pump and another to turn off the pump if the returning water was to cold. Something to do with it putting out the fire and also the condensation on the backboiler was corrosive to the backboiler, and also the pump might pump all the hot water away as well. It was in the bad old days when coal fires ruled and everyone [nearly everyone] had them remember we were a pit village.

[Giant]

I'd say having a thermomstat at all controlling a pump distributing the heat from an uncontrolled heat source like a solid fuel stove, is daft.

 

The pump needs to run all the time the stove is alight.

 

Having turned the thermostat down to the point where the system will always run without hissing and banging, that's pretty much what it does.

 

Agreed. The amount of heat put out will be pretty much the same whether the pump is running or not, so the only saving is in the electricity used by the pump.

 

The amount of heat might be the same, but that doesn't mean you can get good use from that heat. E.g. if it's going into a calorifier coil at the same warm temperature as water already in the tank, it's not going to transfer any heat.

 

Surely it makes sense to try and regulate the supply of water to the back boiler so that it comes out as hot as safely possible, to give best heat transfer to downstream uses.

 

If you must fit a thermostat, then a pipe thermostat fitted close to the boiler outlet will set the pump running whenever the stove is lit.

 

That's basically what we have. The distance is still non-zero.

[Giant]

Mike, sorry, I think I have just realised why you were so incredulous - you were imagining a room thermostat controlling the pump?

 

That would indeed be monumentally stupid.

 

I'm talking rather about a pipe thermostat attached to the hot side pipe coming out of the back boiler.

[Jen-in-Wellies]

Agree that the banging noise is most likely caused by boiling water in the back boiler from poor circulation. The cause could be design of the gravity system, in which case a circulation pump should cure it. Another potential cause is a local air lock in the pipework preventing, or restricting circulation.

 

On my boat, the gravity system goes from the back boiler to its highest point at the calorifier coil. At this point it has the vent to the header tank. From here it drops to the calorifier coil exit and then goes through several finrads, before dropping again to return to the stove. The trim of the boats mean that the finrads go very slightly uphill. If the system is drained and refilled, then a local airlock develops here at the end of the finrads that needs bleeding to ensure that the pipes are full of coolant. Once done, the gravity central heating is completely reilabe.

 

Worth checking on your boat that the radiators and all local high spots in the system are comp!etely clear of air. The trim of the boat bow up may introduce a high point even with the radiators being parallel with the floor. There may be bleed points there, or you may need to carefully open a pipe joint to clear any air. The fact that your return pipes are cold suggests this may be what is going on.

 

If it still happens after bleeding, then look at a redesign of the system, or fitting a circulation pump. Gravity systems can be made to work well. Mine has been for the past nine years, but the design is very restricted.

 

Jenny

[wobbly ollie]

All very helpful folks - many thanks.

I do not have a pump (or thermostat...) of any kind so my first thought, based on the comments received, is to try and improve flow to see if that solves the problem. We don't plan on using the boat much in the winter although I am sure the heating will needed if we do any spring cruising.

 

With the greatest respect to professional plumbers ...I'd quite like to have go at this myself (all part of the fun or new boat ownership) and I'm a fast learner/good listener....

 

So my thoughts are to drain the system, flush it through with maybe a Fernox product and start again.

 

Questions....

1. never drained a system before so any outline instructions would be helpful.

2. would the fire need to be going in order to get the water flowing..? How else would the water drain out?

3. If the fire is burning is there a danger of damaging the back boiler as the system drains?

4. Should I expect there to be anti freeze in the system - I hear mixed opinions on this...

5. Am I right is thinking this shouldn't be that difficult?

 

Thanks again

[BWM]

How is the pipework fixed ? With the brass munson clips, pipework can creak when expanding sometimes.

[mross]

Don't run the fire while draining as you could damage the back boiler. The Fernox has to left in for several days. It's a good idea to use anti-freeze but not more than 25% as it reduces the heat transfer. Drain at the lowest point on the system and use a wet vac to suck up water from a bowl or bucket.

[wobbly ollie]

How is the pipework fixed ? With the brass munson clips, pipework can creak when expanding sometimes.

The pipes are fixed with loose fitting brass pipe clips

 

Don't run the fire while draining as you could damage the back boiler. The Fernox has to left in for several days. It's a good idea to use anti-freeze but not more than 25% as it reduces the heat transfer. Drain at the lowest point on the system and use a wet vac to suck up water from a bowl or bucket.

 

I guess that would be the bottom of the rad?

[WotEver]

I guess that would be the bottom of the rad?

Or where the return pipe connects to the back boiler?

[mross]

As near the stern as possible so, may be, on the calorifier? Where is the stove Wobbley? Front, middle or aft?

[wobbly ollie]

No calorifier. The stove is aft.

[cereal tiller]

No calorifier. The stove is aft.

Have you moved it?

 

Seem to remember your Stove being located at the Bow end

 

CT