I'm Looking for a Simple Switching Solution

[cygnusv]

I have central heating throughout our boat, but it's never before been used to supply domestic hot water for showers etc. We've previously used mains (shore power) water heating with an immersion heater. Having just replaced our solid fuel heater with a bigger better model we now have sufficient heat to supply our domestic requirements. I do though, have a bit of a problem.

Because solid fuel is not as controllable as say gas or electric heating, the output from the back boiler will always fluctuate. Because of this I fitted a zone valve into the hot water pipe from the stove to the hot water cylinder. The plan was for the zone valve to open at 45-50 centigrade and stay open until the fire cools below the set temperature. This is important because the immersion heater is still used, but cuts out just below the zone valve temperature setting. I don't want a situation where if the stove is off I'm inadvertantly using the immersion heater to warm the boat!

So to condense all that I would like your thoughts on a simple but automatic on/off pipe switch that will come on and open the zone valve at 45-50C and stay on until the pipe temperature drops below that setting.

Many thanks in advance, Stu

 

[Martaine2005]

Most conventional heating systems run with two or three port valves. You’d have a cylinder stat and wall stat. These stats would control the automatic port valves.

Martin

 

[cygnusv]

Hi Martin,

Many thanks for your reply. If our heating was purely gas or electric the cylinder and wall stat would maintain the circulating water temperature up to a preset temperature. It would do this by opening and closing the various ports. If all the ports were closed, the boiler would use its own stat to prevent the whole thing going into meltdown. This will not work with a simple solid fuel stove where the controls are all manual.

A far as the domestic water for washing is concerned, I don't want the port to open until the water in the system is at least 45C so as not to drag DOWN the temperature from the immersion heater. I want the back boiler in the fire to take over from the immersion when the fire is hot enough. Even when going flat out, the water from the back boiler never goes above 75C so overheating the hot water tank is not possible anyway. THe hot water tank is a vented calorifier.

I'm thinking of a preset thermal switch to overrule the pipestat. I'm even thinking of maybe bypassing the pipstat altogether by routing through the thermal switch as long as this is considered safe.

Any further thoughts, many thanks. Stu

 

[Alec_t]

If you have a pipe-stat monitoring the boiler temperature, when it opens the valve it could also switch off the immersion heater.

 

[cygnusv]

Many thanks. How would I achieve that?

 

[Alec_t]

Use a boiler pipe-stat which has a SPDT switch and closes the NO contact when the boiler is hot. The NO contact enables the valve. The NC contact enables an SSR to activate the immersion heater.