Understanding Low Limit Pipe Stat Wiring

[Cygnus]

Hi everyone,

I'm new here and hoping I can get some help with a Honeywell L641B1004 pipe Stat. I have looked through the forum and found threads similar to what I need but not a definite match.

I live on a boat and have a woodburner for heating in winter. This supplies heat to 3 radiators. I've recently connected a calorifier to the system, which is a glorified hot water cylinder with internal coil. The problem is this. Because the central heating is a small system, it is very basic. When the fire is lit, the pump runs continuously. This works fine until you add a requirement for storing hot water from the backboiler to the hot water cylinder.

As the fire gets cooler overnight, I want to disconnect the HW cylinder from the cooling water in the heating circuit. I've done this by adding a Honeywell zone valve. Currently, the ZV is being manually operated on a separate switch.

I've just bought a Honeywell L641B1004 low limit Pipe Stat. It was my understanding that if I set the stat to 40C, it would not operate the ZV until the pipe rose to 40C. I understood this as 'make on rise'. Am I misunderstanding this?

I've used a multimeter across common and contact 1 and the stat doesn't seem to be following the rules.

Can anyone clarify this for me please?

Many thanks in advance, Cygnus

 

[AndyPRK]

So you are wanting something to control the hw some valve automatically ?

If it’s a bare metal tank or has a stat built in. Use that to control the valve.

A pipe stat should have both types of contacts. What pipe were you going to put it on ?

Edit. So as the pipe is cooler at night you want the tank valve to stay shut.

You should be able to do that. As long as the temperature range of the stat is suitable. Set it 50C would you ?

 

[Cygnus]

So you are wanting something to control the hw some valve automatically ?

If it’s a bare metal tank or has a stat built in. Use that to control the valve.

A pipe stat should have both types of contacts. What pipe were you going to put it on ?

Edit. So as the pipe is cooler at night you want the tank valve to stay shut.

Hi Andy.

All I want is for the stat NOT to open the zone valve until the water in the heating system gets to 40C and STAY open until the system cools overnight and then close the ZV at 40C.

I'm just trying to keep the water temperature in the hot water cylinder at a usable temperature while the boiler goes up and down.
I do have an immersion heater, but why use that when I have plenty of spare heat from the fire?

Thank you so far. C

 

[Johnmdc]

Common and 1 BREAK on rise.
Common and 2 MAKE on rise.
So to do what you want connect to common and 2.
But I don't think that is a good way of doing it.
What controls have you got to stop it getting too hot?
The valve should be controlled by a cylinder thermostat that will close it when it reaches the set temperature.

 

[Cygnus]

Common and 1 BREAK on rise.
Common and 2 MAKE on rise.
So to do what you want connect to common and 2.
But I don't think that is a good way of doing it.
What controls have you got to stop it getting too hot?
The valve should be controlled by a cylinder thermostat that will close it when it reaches the set temperature.

Thank you. This is really helpful! The way I read the the instructions was 180 degrees out! Massively helpful.
For information. Our boat is only 30 feet long, and the entire Heating circuit is only about 3 gallons. With the fire going full belt the pipe thermometer NEVER gets above 70C. Overheating is not a problem. Also, as live aboards, the heating is always kept low if we go out.
As I said in the original post. It is a very simple system. Though for safety we utilise 2 pumps. One 24 volts, and the other mains from shore power. In the event of a power cut we also have an automatic change over device that switches to inverter generated 230volts. Basically triple redundancy. The 24 volt pump, which is noisy compared to the mains unit, is manually operated. The first radiator in the system is a gravity rad.

Based on your advice I'm going to do a dry run using 'C' and '2' this weekend with a multimeter.

I'll post my results. Many thanks

 

[ericmark]

Are you 12 or 24 volt, I know my son had problems finding 12 volt stuff. However on the plus side not worried about some one touching terminals.

So how are the two pumps linked, I assume twin pumps as you can't have water boiling, he ended up with sensors everywhere, had it been 24 volt there would have been more options.

It is not so bad in a house, you height, and thermo syphon, but in a boat you rely on pumps, so 230 volt needs shore supply or inverter both can fail with desirous results, so what system to you have?

 

[Cygnus]

The boat is 24 volt, but the heating control gear is all mains driven, either from shore power or our sine wave inverter. As live aboards we spend more time on our mooring than cruising but our Trojan battery bank and Victron electronics, which includes solar mppt etc, gives us a secondary source of mains power.

We prefer not to use the backup 24 volt pump for the heating circuit because it is much noisier than the virtually silent mains pump.

Works for us, but trying to conserve heat in the calorifier when the stove cools.

 

[Cygnus]

Thank you all especially johnmdc. I've fitted the Honeywell and it's sorted the problem wired the right way.
Many thanks again, Cygnus