Which pipe thermostat?

[lettherebelight]

Hi all, I have a wood burning stove with a back boiler piped to heat a vented, indirect hot water tank, 28mm pipe work.this was meant to be a gravity system but because of the way it was routed it did not work. I have now fitted a pump which works fine. I want to fit a pipe stat to stop the pump when the wood burner is not being used, ie I do not want to pump cold water. Having been on the Honeywell site I can not find a suitable stat can you help please. Thanks Jason.

 

[Agile]

Is your pump on the flow or the return?

Do you have a rad on the circuit?

Do you have an F&E tank? If so what is it made of?

Tony

 

[Richardthe3rd]

Hi all, I have a wood burning stove with a back boiler piped to heat a vented, indirect hot water tank, 28mm pipe work.this was meant to be a gravity system but because of the way it was routed it did not work. I have now fitted a pump which works fine. I want to fit a pipe stat to stop the pump when the wood burner is not being used, ie I do not want to pump cold water. Having been on the Honeywell site I can not find a suitable stat can you help please. Thanks Jason.

You really need a gravity system on any stove of this nature or a very large heat-leak at least. Page 17 on the following instructions details a High & Low temperature thermostat setup, this being used on a standard gravity system & will control an over heat situation & protect the stove against cold circulation.
http://www.woodwarmstoves.co.uk/_assets/manuals/new instructions fireview march 2010.pdf

Honeywell pipe thermostats would be my choice.
HTH

 

[lettherebelight]

Agile,
Pump is on the return.

There is no rad, but it is a big house and the wood burner goes into 4 normal sized domestic water tanks piped in parallel and is not the main source of heating the water just a helping hand, so to speak.

The tank is plastic but is not getting excessively hot.

Richard.

I would like to use Honeywell pipe stat but their blurb says low limit contacts make on temp fall.
High limit break on temp rise.
I need something that will break on temp fall, which is why I am stumped. Unless I am being really dumb and missing something.

Regards Jason.

 

[Agile]

Because you do not have a rad its considered that in an extreme case with a power failure that the boiler could boil.

In that case a plastic F&E tank is going to get up to boiling point.

Although current plastic tanks should be rated to manage that, its only when its correctly supported on a flat base.

A metal or fibreglass tank is safer!

Tony

 

[mfarrow]

I need something that will break on temp fall, which is why I am stumped. Unless I am being really dumb and missing something.

How would you intend to detect the water's getting hot without any flow in the pipe? Or would you turn the pump on manually?

There seems to be a solution in the form of a flue thermostat: http://www.stovesonline.co.uk/wood_burning_stoves/Flue-thermostats.html

 

[Agile]

Most pipe stats are changeover microswitches.

Placing a pipe stat within say 300-500 mm of the stove would give enough conduction/gravity circulation to effectively operate the pipe stat.

Tony

 

[ianmcd]

just use any pipe stat and wire a permanent live into the NO contact and the pump live into the C contact and set the pipe stat at around 30 degrees then the pump will only get power at whatever you have set the pipe stat to

 

[lettherebelight]

Thank you all for your help. I think Ians solution my be my best bet, I had thought about it but was not sure if it was safe to do. I'll give it a go. Thank you.

 

[ianmcd]

yes it is safe to do the only problem you have is in the case of a power failure, as you have said that the gravity HW method didnt work, then you should create another method of expansion in the event of power failure, by your user name if a Tubel cain would be of any help then please feel free to PM me and I will assist you in any way I can

 

[lettherebelight]

Just to let you know I wired up the pipe stat as Ian suggested placed it 450mm away from the Morso and every thing is now working fine. Again thank you Ian.

 

[Norcon]

I need something that will break on temp fall, which is why I am stumped. Unless I am being really dumb and missing something.

How would you intend to detect the water's getting hot without any flow in the pipe? Or would you turn the pump on manually?

There seems to be a solution in the form of a flue thermostat: http://www.stovesonline.co.uk/wood_burning_stoves/Flue-thermostats.html[/QUOTE]

A flue stat is normally used with a loading unit where the sf boiler is heating a large thermal store or accumulator.
The load unit then takes care of the return temperature and some (like the Laddomat) also allow gravity circulation in case off a power failure.

The flue stat on its own cannot prevent cold water entering the boiler casing and lowering the efficiency.
Just the same as a pipe stat on the flow will not either.

The earlier link posted with the Woodwarm instructions is how it should be done.
Should be no pumps or valves on the primary return to a stove.

 

[Richardthe3rd]

Madness not having some form of heat leak!!

 

[lettherebelight]

Having run the system for a few day the only comment I would add is setting the stat at 30c was much to low and was acting as a heat sink at night when the fire died down causing the tanks to cool down to much over night. Setting the stat to 60-70C solved the problem.