Load valves for back boilers

[Stereo]

A bit off topic but I know there a load of people with wood burning installs here so have a quick Q. I have an Esse W23 connected to a thermal store and underfloor heating. The store is also connected to a condensing gas boiler via a coil which keeps it at a set min temp. Problem I have is that when I light the stove, the water at the bottom of the store is below this min temp and that means cold water coming back to the stove = poor running, gumming up and a messy flue. Apparently they should have put in a load valve when fitted but didn't bother.

 

So I need one. A plumber I know has recommended a passive one which I assume is just a bi-metalic strip system or something which will return water to the back boiler until it reaches 60 deg and then starts letting it into the store. This means only hot water goes into the top of the store (better stratification?) and also cold water is not allowed back in the back boiler. I am told I will need a pump with this too as it's all gravity at the moment. What happens if the pump fails / power cut?

 

I've also seen the powered laddomat type ones which are the same concept but contain an internal pump (I think).

 

Anyone use either of these and offer comments? The plumber seems to think that the passive one will need a flue sensor to operate it but surely it works on internal water temp?

 

Thanks for any comments and sorry for the OT. Spent a lot of money on their rig and it doesn't work well so need it get it right before spending more and I'm losing trust in 'experts'.

[Breezeblock]

I have a laddomat one on our boiler and they are essential to stop them from running too cold it sounds like you should deffo have 1 fitted all it does is pump around until it reaches a preset temp then bleeds in cold water at a sufficient enough rate to stop overcooling off the boiler

[IRE David H]

be careful though if it gets too hot it could explode due to steaqm pressure, now while it shouldnt happen with a load valve dont put in a lever or gate valve

[cornish wood burner]

Your plumbers idea is to keep the flue temperature up which equates to good combustion. Just a different system of achieving the required result.

[openspaceman]

So I need one. A plumber I know has recommended a passive one which I assume is just a bi-metalic strip system or something which will return water to the back boiler until it reaches 60 deg and then starts letting it into the store. .

 

The ones I have seen use a waxstat just as used in a car coolant circuit, it also has the same purpose of getting the stove up to working temperature as soon as possible.

 

 

This means only hot water goes into the top of the store (better stratification?).

 

Yes but I would expect a gravity system to do the same..

 

and also cold water is not allowed back in the back boiler. I am told I will need a pump with this too as it's all gravity at the moment. What happens if the pump fails / power cut?.

 

Your gravity system should be vented and adding a pump won't affect that, you must allow a direct vertical path to the F&E tank still.

 

I've also seen the powered laddomat type ones which are the same concept but contain an internal pump (I think).

 

Sort of: the back end protection pump has the thermostat built in, the hot water is constantly circulated from hot output to cold return until the thermostat starts opening at about 60C and let some hot water into the main heating circuit, once the thermostat is fully open it nearly blocks this bypass circuit so all the water goes to the main heating circuit..

 

Anyone use either of these and offer comments? The plumber seems to think that the passive one will need a flue sensor to operate it but surely it works on internal water temp?

 

 

It makes sense to keep the flue gas temperature up to its operating temperature as soon as possible but I have only seen the basic laddomat type and can't picture how sensing this could control the pump unless it modulates the pump speed.

[cornish wood burner]

Fairly sure the 3 port valve would just be driven by the flue stat instead of the pipe stat.

A system more "in touch"with the fire perhaps.

[openspaceman]

Fairly sure the 3 port valve would just be driven by the flue stat instead of the pipe stat.

A system more "in touch"with the fire perhaps.

 

Yes. I would worry about the granularity of the control, i.e. would the valve suddenly open once the flue temperature went above, say 110C and fill the bolier with cold water? It needs to gradually let in a bit of cold so as not to yoyo between hot and cold, the laddomat seems to do that smoothly.

[cornish wood burner]

Yes. I would worry about the granularity of the control, i.e. would the valve suddenly open once the flue temperature went above, say 110C and fill the bolier with cold water? It needs to gradually let in a bit of cold so as not to yoyo between hot and cold, the laddomat seems to do that smoothly.

That's what I was thinking last night after my post, too much hysteresis as you say, controlling it that way. I had a dig this morning and (fairly sure again)I did get that wrong. I found an ESBE LTC load unit that uses or can use a flue stat to drive the pump. I think their idea is to turn the pump off when the fire goes out so the fire doesn't then act like a radiator and drain the heat from the store.

There is still a thermostatic valve in the system to control water temp which makes more sense.

[Stereo]

Thanks for all the comments. From further reading it seems that the temp range in the store is important. At the moment, as soon as I light the fire and water starts circulation, I putting potentially cool water in the top of the tank which ruins the 'stratification', I think. Not only that but I am also dragging the coldest water into the boiler, so ruining the effectiveness of the stove.

 

I now gather that I would need a flu sensor to control only the pump, as mentioned above. It will only run when the fire is lit and that makes sense of course. I have the same concern with a passive valve as above too. Will it just pop open and let all the cold to the boiler and then shut again when it gets it back? The active type devices seem to open and close more gradually.

 

I guess I need to ask the manufacturers themselves.

[Stereo]

OK, starting to worry now. This appears to be the store I have:

 

http://www.heatandplumb.com/images/products/gledhill/main/main_product_GHSOL021.jpg

 

My Esse is connected to the 'Conventional Heat Source' connectors as pictured. I have always wondered why the flow is so low on the tank as it would make sense to have it at the top. I also assumed that the Esse was using the same water as that in the tank. However, this image seems to suggest that the Esse is running into a coil and therefore a sealed circuit. I thought this was not allowed for uncontrolled sources?