Central Heating - Pump Off

[WJM]

Picking up a piece from this month's Canal Boat Mag;

 

By extraordinary coincidence - last week my CH welled up and spat about 6 litres of fluid out through the header expansion tank and I have been a bit bewildered as to why - and this month a Reader's Letter seeks an answer to the exact same problem.

 

The advice given is - never run your stove (with back-boiler) with the CH pump switched off because you get a build up of heat that boils the system causing the overflow. I was under the impression it was ok to use the stove independently of the CH (I have a Lockgate 'silver cylinder' stove) - who is right?

 

 

Also - I guess I must have 5 or 6 litres of water/anti-freeze mix sloshing about somewhere - should I be concerned about that?

[John Orentas]

Not such a coincidence, it is quite a common occurrence, local boiling will inevitably cause the sudden explosive effect you describe, we have had several people on here who have attempted to control cabin temperature by switching the circulation pump from a thermostat. When you think about it, clearly the wrong thing to do. You must maintain a flow of water through the back boiler as long as there is a significant fire on the go.

Edited January 9, 2007 by John Orentas

[bottle]

Hi

 

I have also read that letter and I think it explains it quite well, With a normally pumped system the pipes are of 'small' bore compared to a convection system.

 

The water in the back boiler heats up but cannot dissipate that heat quick enough (pipes will not allow fast enough flow).

 

The water in the back boiler begins to boil and/or turn into steam, the high pressure then overcomes the resistance of the pipes (to flow) and water is expelled into the expansion tank.

 

The answer also suggests a 'pipe stat' near the back boiler so that when the water in the tank reaches a high temperature it will turn on the pump so alleviating the problem. A good idea I think.

 

[canalcruiser]

The answer also suggests a 'pipe stat' near the back boiler so that when the water in the tank reaches a high temperature it will turn on the pump so alleviating the problem. A good idea I think.

 

 

Having recently fitted a Pipe Thermostat on my central heating system I agree that it does control the running of the circulating pump. The pump only runs when the water temperature is above that set on the themostat. When the temperature falls the pump stops. Thus conserving battery life as the pump only runs when needed

 

Chris

[Pirate]

If I were to leave my fire on without the pump it would shut the fire off at a certain temperature and it works I tried it lol

[Tony Brooks]

If I were to leave my fire on without the pump it would shut the fire off at a certain temperature and it works I tried it lol

 

 

Yes, but you must either have an "expensive" stove with a thermostatic ait valve (Like my old Parkray and unlike my Hunter & Brunel) or a fusable plug on the boiler. I doubt you have the latter because it creates a hell of a mess when the fire goes out!

 

Most of the "normal" stoves fitted to boats are not fitted with thermoststic air valve.

 

 

 

Anyway thanks all for for probably unintended the feedback. Its good to know the Q&As are helping at least one person.

 

Tony Brooks

[WJM]

OK - excuse the non-techno-speak

 

I have a thin curly copper pipe/wire coming from the control unit and ending in a copper bulb that is attached to one of the water pipes at the back - what is this?

 

 

 

Thinking further; and dont laugh - a while back my stove kept switching itself off - I actually saw it do it once - I saw the lever pop up - so I took to hanging a bunch of keys on the lever to keep the stove on - ok, ok even before I know why I can guess this was probably not the best thing to do, but it kept me warm!

[bottle]

OK - excuse the non-techno-speak

 

I have a thin curly copper pipe/wire coming from the control unit and ending in a copper bulb that is attached to one of the water pipes at the back - what is this? The bulb is a heat sensor when the pipe it is attached to reaches a certain temperature it will operate a switch in the control unit, As to what switch it operates is open to conjecture but I suspect it will turn on your pump or turn off the fuel supply.

Some one on here will know which.

 

 

Thinking further; and dont laugh - a while back my stove kept switching itself off - I actually saw it do it once - I saw the lever pop up - so I took to hanging a bunch of keys on the lever to keep the stove on - ok, ok even before I know why I can guess this was probably not the best thing to do, but it kept me warm! If the fire turned it self off it was for safety reasons but it could be a faulty sensor.

 

I think your system needs checking by a qualified engineer. Bypassing a safety mechanism is a no no, it should be checked a s a p.

[WJM]

thanks bottle

 

playing detective - I was running the stove with the CH pump off coz i didnt really want the rads on. Methinks the heat sensor was reading the overheat on the static water and turning off the fuel supply - that was the 'switch off' that I saw - then when I hung the keys on the switch it forced the fuel supply to stay on and the whole thing to boil!

 

Lesson - dont hang keys on control levers!

 

What about the slop now in the bottom of the boat - somewhere! - how do I get it out - or can I ignore it and wait for it to evaporate?

Edited January 10, 2007 by WJM

[bottle]

If you can get to it use a 'wet and dry' vacuum cleaner.

 

Then cloth/rag etc. and ventilation, forced if neccessary (fan).

[Tony Brooks]

OK - excuse the non-techno-speak

 

I have a thin curly copper pipe/wire coming from the control unit and ending in a copper bulb that is attached to one of the water pipes at the back - what is this?

 

snip

 

It is a capilliary tube. Although you probably can not see it there is a metal bulb full of methanol (dare not say alcohol around here in case it gives anyone ideas) recessed into the boiler. The other end of the tube goes to a pair of metal bellows (old fasioned engine thermostat type) at the top of the rod. As the alcohol evaporates the pressure expand sthe bellows and shuts the air damper.

 

If you have a graduated control knob it pre-loads the bellow so they havevto expand more/less to shut the valve.

 

You probably have an adjustment where the actual air valve plate is fitted to the rod and this can be used to close the valve at different temperatures (so no need for the keys perhaps). On a my Parkray the adjustment was set so you had a gap when the stove was cold just as wide as the diameter of a florin (2 bob piece).

 

As your stove shuts itself down in response to boiler temperature you may find some thermo-siphoning, even on 15mm pipe, but I doubt it would be much unless the "hot" pipe ran right up to ten roof, and that's silly.

 

 

 

Tony Brooks