Log burner back boiler only heating radiators

[Squaredy]

3 hours ago, scoobysrt said:

Is your radiator system as I describe with the only difference of having a pump?

Off the top of my head I am not quite sure. 

 

There is a small rad in the airing cupboard directly above the woodburner which gets hot through gravity.  The pump is also in the airing cupboard and the header tank (which is metal) is also at the top of the airing cupboard.  It is a very simple system, but you have to assume it will boil occasionally (if you have a power cut and the pump is off for example).  So it needs to be designed to allow for this, with no plastic pipework.

[slack ma girdle]

I have a gravity feed system ,  that runs two radiators,  one upstairs . I didn't install it, but it has two 28mm pipes out the back of the stove,  and 28mm all the way to the header tank in the loft. The return reduces to 19mm about two thirds of the way to the top. Both radiators T off these pipes.

I am not sure if this makes sense as i don't know what I am talking about .

Some terrible pictures below.

[scoobysrt]

Thanks guys, becoming quite clear now.

 

I presume if I use a pump I don't have to have all the pipework on a rise, I know the vent needs to go straight up and have no valves or pumps in the way but if I was to now decide to have a water tank to do the hot water that could be upstairs but not directly above the room the boiler is in.

 

The hot tank would be in an airing cupboard in one of the bedrooms which would make it impossible to have a rise on the pipe and instead it would have to be horizontal under the floor boards but as I say presumably a pump negates the need for the rise.

 

Time ran away from me today but I will put a drawing together to show what I'm trying to achieve and whether I'm on the right track or not.

[Peasgood]

I'm not a plumber but have had plenty of backboilers and gravity systems over the years. 

I would think the fact the pipework is going upstairs from a downstairs fire means you have a rise and horizontal pipework under the floorboards wouldn't matter. Had plenty of systems that worked off gravity over large areas and no way did the fitters laser level that pipework to get a constant rise. The nature of the gravity system will drive the flow.

Having said that, I would still fit a pump, if you don't the first rad will get hot, second not so much and last one is a waste of time.

Personally I would design it with two circuits, one for hot water and one for heating. Simple thermostat on the pipework that turns the pump on when it gets to a set temp and goes off when it cools down. Lashings of hot water whenever needed. Not sure how/why you don't use hot water but it isn't a waste to have it, it only heats and stays there it doesn't escape, especially useful in an airing cupboard.

I asked my plumber to fit a system that works exactly this way and he goes and fits Hive controllers, motorised valves and allsorts. God knows why as it over complicates it and at the mo if only the oil is on I can't even fill a sink with hot water! (fire part works fine)

[Steven P]

Hot water tank.... often seen as 'inefficient' because the heat escapes from it... but that heat escape is also heating a room in the winter, so it is like a small radiator. Only inefficient in the summer when you don't want to heat a room.... but will you use the immersion heater in the summer so no change there?

[Muddy42]

I’d love to see a diagram of a hot water and radiator system back boiler from a stove if possible?  I’m helping renovate a rental cottage which I think has such a system, but the former occupiers didn’t use it.  I'm doing the heavy lifting/woodwork and organizing the other trades like plumbing and electric.  It’s a small two story cottage without any obvious heat pump.  I think I understand the concept that (unlike gas/oil central heating) it needs a vent/pressure/heat release in case the stove gets too hot. The person who lived in the property 10 years ago says it used to work fine – lots of hot water and warm radiators.  If the system got to hot, he said you could hear it boiler off in the attic.  But who knows what has happened since then. The attic is very hard to get into and had bees in it (!), so I haven't been up there yet.

 

I am concerned that it might be too much of a ‘hands-on’ system for modern millennial tenants, who want guaranteed instant heat and hot water. So the system would need to work in tandem with electric.  But if its working, I am loath to remove the system, purely because it would be so hard to replicate.

[Rob_the_Sparky]

My only concern with a pumped system would be what happens if the power fails?  If you lose the ability to pump is it safe?  No idea how to make it safe but I'd guess there must be a reasonable solution if you plan for this happening.

[GarethM]

Sadly no system like that relying on a pump is safe. Proper log boilers are built with heat storage and a mains cooling loop for that reason, in the even of the thing boiling it safely vents and cools down before it burns down without any electrical inputs.

 

I should say I've had a baxi with a backboiler and learnt from experience that it's not the greatest idea.

Edited November 20, 2023 by GarethM

[slim reaper]

Really need to know the boiler output and size the rads accordingly. I know from experience that non rising gravity pipework is a recipe for pain in the arris airlocks

[Muddy42]

1 hour ago, GarethM said:

Sadly no system like that relying on a pump is safe. Proper log boilers are built with heat storage and a mains cooling loop for that reason, in the even of the thing boiling it safely vents and cools down before it burns down without any electrical inputs.

 

I should say I've had a baxi with a backboiler and learnt from experience that it's not the greatest idea.

yes that makes sense.  

 

If It helps, my eco angus log boiler has three safety features.  This is basically a jacket of water around a furnace which is pumped via a flow and return loop and the heat is exchanged into storage tanks. Firstly once the water reaches a set temperature the fan turns off and slows the fire down.  Secondly if the jacket of hot water gets too hot, it will trigger a value which dumps the hot water out of the loop.  This seems to happen if I set the temperature too high (say 90c) and don't have the radiators on enough (if its seriously cold and the radiators are on 24/7 90c is fine).  I've never seen the third feature in action, but I can see the boiler is connected to the cold water supply - if triggered cold water floods in and cools the boiler somehow.

 

In a power cut I guess the fan would stop working, and so would the pump, but the two valves would still provide a safety net.