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hot water flow from fire back boiler - pipe stat/pump wiring

Postby jackie weaver » Tue Nov 25, 2008 4:19 pm

HELP please

I have installed a lovely big multifuel fire with back boiler. The plumber came and did the pipe work, attached 2 rads. I have not been able to get a electrican so the port valve is kept on open (have no choice) and the pump i have to switch on, it works fine and gives out the heat etc. BUT

my plumber has now found me an electrician, and when saying where he would put a pipe stat, on one of the pipes behind the fire, i have realised that there seems to be a problems with that, i phoned my plumber to ask but he doesn't really want to know.
Firstly, with no pump on, water quickly heats up one pipe and this follows the gravity fed, but this is actually the pipe the plumber has chosen as the retun pipe.
How does a boiler box know which which pipe to flow out of, they are level behind the fire?
When you put the pump on, because of the cold water in the system, they immediately cool right down, so hence this makes me think the pump would be fooled into being switch off again, even right behind the fire they are only mildy warm due to the cold water flow through.
The stat starts at 50 degrees, so i cannot work out how it will make the pump work as these pipes take hours to heat up whilst being circulated round, which is by a pump, that if wired in, i am sure would think, pipes are not at 50, so dont switch on!!
Can you see my dilema, or i am mad and completly missed the point?
If i am right, then i am happy to switch the pump on manually, have the port wired so it heats the hot water first then does the rads, but what could i do to switch the pump off when the fire goes down low, as the pump would run all night, as it does now (unless i get up in the middle of the night and swtich it off), is this bad for it to run contstantly? could we use a room thermastat to acheive this?
Sorry so long, but would be sooooooooooo appreciative of help on this as i am stuck and dont want to pay for electical work that i cant think will make this automated at all.
jackie weaver
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Simply Build It

Postby plumbbob » Tue Nov 25, 2008 8:44 pm

I can see what you mean, but first of all, what type of fuels are being used, because it makes a very great difference on how it is connected especially from a safety point of view. What else is connected to the system?

On a gravity system, the highest pipe is the flow and pipes shouldn't run horizontally from the boiler. Logical really but as your system is not designed as gravity (or is it?) it horizontal pipes are ok, but it is a little of a worry that the return gets hot first!
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Postby jackie weaver » Wed Nov 26, 2008 2:11 pm

Hi Plumbob,
thanks for trying to help me.
I will try to answer the questions
I burn wood on the stove
It is connected to the hot water cylinder via the coil etc. and then a large rad and also a bathroom ladder rad.
On the back of the fire the short length of pipe coming out the back of the fire from the boiler inside are level, and the plumber has evenly put them to both rise up hill, thru the wall and then gradual uphil for gravity feed. He has also installed a good over flow thing incase of a power cut.
As the fire boiler inside the fire is put in level, by putting on of the out higher, would that be able to encourage it to be the flow?? But saying that, as soon as the pump would kick in, the pipes would go nearly cold again, so would still switch off again wouldn't it?
thanks again, i hope we are getting somewhere
jackie weaver
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Postby alanfr » Wed Dec 03, 2008 5:40 pm


Usually the gravity feed will flow from a point high in the boiler (to the upper tapping in cylinder) and return to a point low in the boiler. This is basic requirement of gravity feed. Most boilers have 4 tappings - 2 are for gravity and 2 are for pumped. The pipe stat is put on the gravity return pipe. Are you sure your plumber has told you correctly which is he return? From your description the plumbing is wrong! But apparently it works somehow???
If the connections are correct then the pipe stat will switch on the pump as soon as your water in the cylinder exceeds the desired temperature set on the stat (at which time the water out of the boiler will be hotter and the water in the tank is hot).
When the pump starts it should be pulling water from another top boiler feed and pumping it round the ch system to a bottom boiler tapping. Although cold water will be pushed in to the bottom boiler tapping it is unlikely to upset the pipe stat as firstly this water will be heated inside the boiler before it reaches the higher level, secondly the gravity feed will reduce to zero (water only rises if it is pumped or if it is hotter that the water above it) and thirdly in any event the water would be heated by the cylinder water before hitting the return pipe anyway.
Sorry for long reply but hope it helps. If you want to exchange emails please reply saying so - I can send some diagrams and you can send me how your system seems to go together.
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