Boat Central Heating

[Scratchy El Snippetos]

Hello There,

I have a Kabola diesel stove on my boat with a back boiler which runs to three radiators.

None of the rads are getting hot and I am worried that the circulation pump the boatyard sold me is too powerful and that the water is moving too fast and thus not getting a chance to heat up in the boiler. Does this sound possible?

I have gone through all the usual bleeding procedures and scoured this and the waterways group to make sure everything is set up right on the system.

The Jabsco circulation pump I have does not have a speed control, so would I be able to slow the flow down by closing the lock shield valves on the rads? I have tried this and found the noise of the pump changes, not sure if this would achieve the desired effect.

Thanks

Scratch

[Grunff]

No. It just doesn't work that way - water can't be pumped round the system too fast.

Are you certain water is being circulated through the radiators? Any chance there is a blockage? Or they're sludged up? Is this a new system?

No, again it just doesn't work that way.

No, it wouldn't.

How about a description of the system, and its history?

[Diesel Miser]

Have you thought about lighting it ???? g&ducks dm

[Jim]

If you have a dual Heating System on boat ie Engine heats water for Domestic and CH System , try turning your Circulation Pump when engine is running . If Rads get Hot it cannot be the Pump or Air blocking rads .

[Canaldrifter]

1. Check water level in system is OK

1. Bleed rads with pump running.

2. Ensure pump is fitted so the flow goes the right way round. There is an arrow on the casing. Heat wants to rise, so arrow should be in direction of hot flow on the flow side, or return flow on the return side. (It is surprising how often installers get this wrong.)

1. If the system is a single pipe circuit, that is the entire circuit goes through each rad one at a time, and not a two pipe flow and return circuit where each rad is fed separately from the flow pipe, make sure none of the rad valves are stuck closed. This can happen if thermostatic valves are fitted. They should not be fitted to a single pipe system. A gentle clout with a hammer might clear them, otherwise try tapping down on the spindle beneath the valve head, or pulling it up with pliers. The head should unscrew.

2. If above all OK and system doesn't circulate, isolate pump (valves either side) or drain down system and remove pump. Run it briefly and make sure impellor is actually attached to the spindle and turns.

1. If none of the above work, Scratch head....

Tony H (with ex-plumbing and heating engineer's hat on)

[Bozo]

Be careful if shutting valves on radiators, especially if it is a single pipe system. If the water can not circulate and the boiler is on you are in danger of boiling the water in the boiler, this creates a lot of steam and possibly pressure.

[Adrian Stott]

You should have a (pipe) thermostat in the system. Since you haven't mentioned one, and given the reported systems, I assume you don't?

This should be attached to the output (hot) water pipe, as close to the Kabola as you can get it (no more than a few cm away).

Its purpose is to control the circulating pump. It turns the pump on only when the water in the Kabola has reached maximum temperature (about 90C), and turns it off when the water temperature has dropped to ~50C.

This ensures that the water sent to the radiators is always hot enough to be useful! It also saves electricity, and wear on the pump, as the pump will run only about 1/4 or 1/3 of the time.

You do *not* need to worry about the speed of the pump!

Pipe thermostats sell for about a tenner at most plumbing shops. The wiring is simple (although I added a circuit bypassing the thermostat, with a manual switch, so I could test the pump easily).

Without a thermostat, the pump runs all the time, keeping busy circulating tepid water.

Adrian

Adrian Stott [e-mail]

07956-299966

[Canaldrifter]

Same applies when using a 12v roomstat.

The danger with this is when the pump is turned off by the stat the water won't circulate through the back boiler, and will boil, causing problems. Stats are designed to be used with gas or oil boilers that are also turned off when not required, thus not boiling the water.

An atmospheric header tank feed pipe should be connected to the CH return pipework close to the back boiler, certainly without any kind of valve or pump between it and the back boiler, to take up expansion.

If the fire is hot and water is not boiling in the back boiler (boiler is the wrong term really.... should be heat-exchanger) then either there is no water in the boiler or the water is circulating, in which case, as Adrian says, the flow pipe should be hot and your prpoblem is with the rads or rad valves. (Radiator is the wrong term really.... should be convector).

This is an obvious question, but is the back boiler getting hot enough when the fire is lit? There are no firebricks infront of it absorbing heat and reducing its efficiency?

Tony H

[Scratchy El Snippetos]

Cheers for this, was thinking about a pipe stat...do you think this one would do the job?

pipes etc are never getting more than tepid, even with the stove blazing, away so I think the water needs a decent chance the heat up.

Do I just wire it straight to the circulation pump?

Thanks Again

Scratch

[Robert Laws]

I have a Kabola on my narrowboat and it also feeds three radiators, but it does so by gravity; there is no pump. It uses 22mm pipes throughout. It works well; I have used it for 10 years.

Are you sure there is no air trapped inside the Kabola's back boiler? if there is no vent pipe from the kabola itself this could happen - does it have a bleed screw there? it could also be that the pump is running too hard and drawing air in to the system from the vent pipe/ header tank.

Robert

[Adrian Stott]

Mine is wired that way.

Adrian

Adrian Stott [e-mail]

07956-299966

[Scratchy El Snippetos]

Cheers for the advice. I've managed to source a 12volt stat and will let you know if it works

Cheers again

[Brian Holt]

I have a Jabsco pump and they don't like air in them, you must make sure they are mounted where it is impossible for any air to collect in the impellor. Another point, has anyone added neat antifreeze to the system ?

[Ron Jones]

Why? If I do that at home, the bleed valve slowly sucks air.... (I didn't install the system, it was done by the last owner using a competent(?) plumber...)

[CS]

Pipe thermostats I have found only seem to operate with a max 10 degree differential??

[Canaldrifter]

I'm assuming the pump is installed on the flow side. Obviously your's isn't.

That's OK, but for the reason you have just stated, it is far easier to draw air into the system with it fitted on the return.

Tony H

[Ron Jones]

That explains it. It's a cr*p system anyway. I think it must have been a cheap one - has a naff Primatic hot water tank :-( - means I can't put anything in the system to stop corrosion. I am planning to change it (at the very least put in a normal hot water tank and overflow tank - and then a load of Fernox!)

[Canaldrifter]

Primatic? Are they still making them, or is yours ancient?

Have you considered installing a combination boiler and doing away with water storage altogether?

Don't overdo Fernox.... it can cause corrosion problems in rads if too concentrated.

Tony H

[Adrian Stott]

and overflow tank - and then a

Be sure to get a copper one, as the steel ones are usually too thin to take the pressures generated by a boat domestic water pump.

Marden Cylinders (01484-714516) built mine. I assume it is still in business. It will make them to any shape, size, coil(s) configuration, etc. wanted. When my original (200 litres with two coils and two electric element bosses) one started to leak after several years, Marden decided the problem was due to a fabrication shortcoming and gave me a new one free of charge.

Adrian

Adrian Stott [e-mail]

07956-299966

[CS]

Marden Cylinders have changed hands/business but the core cylinder makers have now set up as DEP Avecombe 01422 372224.