Wyleu, Desperate, Sleepybubble & List,
Thanks for the tips. Is 5mm of 3mm solder enough to fill the capillary space in a 28mm fitting? If so that's a good guide.
I hadn't considered over-fluxing. I guess the flux just needs to be a surface smear to do its job - and not be so excessive that it boils out of the joint.
Having spent the afternoon and evening making sub-assemblies to couple up to the central neutraliser unit, I'm dreading the last two connections on the vertical rising pipes. These will be the one, guaranteed to start spraying water out when I refill the system.
I am also becoming aware that I might also be creating something that cannot easily be un-built. I might put the odd compression coupling in some of the pipes so that at least it can be slackened off and provide a little give, plus an extra degree of rotational movement so that things can be prised apart.
There are the conflicting requirements in a gravity feed system of using big 28mm pipes and keeping all joints and elbows to a minimum so as to maximise flow, then have to add a few 28mm compression couplings so that you can service the unit.
The systemzone neutraliser has 4 big pipe unions along its base and two on either side. This makes it fairly difficult to move in any direction once the unions are tightened.
I'm now 12 hours into this install and aching from kneeling and lying on the floor. I hope to complete everything tomorrow in daylight and then re-fill the system. Otherwise we will be bathing in cold water if I don't get the boiler running again - but I suppose I do have an unused immersion heater that could be used at a pinch.
Attached are a couple of pictures of the work in progress - plus a description below of what the various bits are.
The systemzone is a 10" wide x 6" high x 3" deep steel vessel fitted with a load of 1" BSP unions. Heat from the wood fired boiler is gravity circulated into the left hand side. Heat from a pumped gas boiler circuit is fed into the right hand side. The bottom unions are separate circuits from which heat can be pumped out of the unit to feed a specific zone. Systemlink make these in all sizes to cope with properties that have several zones and several heat sources. I just have 2 heat sources for the moment and one zone.
The vessel is going to get up to boiler temperature - so the airing cupboard will be the hottest spot in the house.
My cat will no doubt find this out soon.
He did however get locked in the loft this evening as a result of his curiosity, and after hearing a mewing noise for some time - he had to be man-handled down the loft ladder which he found quite undignified.
The flow and return from the woodstove boiler come in on the left hand side in 28mm pipe. The flow continues upwards to a 45/45 elbow dog-leg and then as the expansion pipe up to the header tank in the loft. Just above the dog-leg there is a T which feeds the heat-leak radiator in the bedroom.
The return to the WBS is the lower left union on the system zone. It goes down to the WBS, and is also Teed to the return pipe of the heat leak radiator. The return to the WBS is also fitted with an injector T, which can be used to accelerate the flow if the gravity circulation is insufficient. As far as possible I've tried to keep these connections neat and free from unnecessary obstructions. I went out of my way to make sure the expansion pipe to the header tank only had a dog-leg and not a pair of 90 elbows en-route. This way if I do boil the WBS, then the water and steam has a direct route out.
The new green Wilo pump behind the systemzone. This pumps the flow from my gas boiler into the right hand port of the systemzone.
The four lower ports are for two separate zones. The left and right unions are the flow and return to my usual pumped HW and CH circuits. The middle pair will eventually be an additional zone (probably the Lister etc in the shed - when I complete some more pipework).
Whilst it does look a bit of a rats-nest, there was already a considerable amount of pipework already in the airing cupboard, including the original CH circulation pump, the hot water cylinder, the flow and returns to the boiler and central heating loop and also the motorised valves for selecting HW and CH. Adding the systemzone here seemed logical, because it is straight-up the side of the chimney breast from the wood burning stove/boiler.
I hope to have the plumbing completed tomorrow morning and the system re-filled. I also have to move the control electrics from where they are obscured behind the systemzone to a position further up the wall, and also fit a pipe stat for the control of the new pump, to ensure that the heat is circulated out of the systemzone when the wood burning back boiler reaches a sensible temperature.
Now that the bulk of the plumbing is in place, it would be possible to fit a twin coil thermal store on the output of the WBS such that it gravity circulated. This store would probably have to be located in the attic, and until I get around to a long promised loft conversion - this option will have to wait.
Anyone considering a WBS, might wish to consider whether the additional hassle involved with linking a back-boiler into a gas central heating system is really worth the effort. Pipe runs and the limitations of existing building features (such as chimney breasts in the way) can make what appears on paper a simple idea into a bit of a marathon project. You might wish to leave the plumbing to the professionals - unless you have a lot of time and evenings and weekends to pick away at the pipework.
It's slightly ironic that this house started with a solid fuel boiler in the back of the range in the living room, and now after 2 generations of central heating, something similar is going back in.
Ken
