Which tappings to use

[Trevor Smith]

I have an Ideal Mexico boiler and I am going to change the gravity DHW pump ed CH to a fully pumped system, according to the instruction manual I can u se tappings to give me flow across the boiler or either side. At the moment the CH flow & return are on the right hand side and the DHW o n the left, I could take flow from the top right hand side as the distribut ion tube is on this side or would it be more efficient to take the flow fro m the left hand top or would it make no difference.

[harry]

mped CH to a fully pumped system, according to the instruction manual I can use tappings to give me flow across the boiler or either side.

on the left, I could take flow from the top right hand side as the distrib ution tube is on this side or would it be more efficient to take the flow f rom the left hand top or would it make no difference.  Ads not by this si te

It is theoretically slightly more efficient to use "diagonal connections". Eg top right and bottom left. This gives a better distribution of water flow through the boiler. However, your best bet is get rid of the thing, it is long obsolete. (If it's the ancient thing I am thinking of.)

[Trevor Smith]

That is one reason I'm changing to fully pumped because from what I've read modern boilers can't do gravity, though I wont be changing it for couple of years due to funds.

[John Rumm]

There is not enough in it to make any real difference, so use whichever are the easiest to plumb.

If you can arrange for some pump overrun you will get a worthwhile improvement in efficiency on a big cast iron lump like that.

[Trevor Smith]

How would a pump overrun work?

[Bob Minchin]

It would help extract the heat from the cast iron boiler into the rads rather than lose it either into the room with the boiler in or lose it up the flue.

[harry]

The burner goes off but the circulation pump runs on for a few minutes longer to extract heat that would otherwise be lost. There is a massive amount of heat stored in this cast iron lump.

I would say don't bother altering the pipework until you are ready for a new boiler. The new boiler will have a lot of the stuff inside the cabinet that is external/separate to your existing boiler. So there would be a lot of work wasted/need to be redone.

And when you are, don't get a combi boiler, just a straightforward replacement (but condensing so more efficient)

[harry]

BTW. If you are short of cash, consider the "Green Deal". You would get a new boiler & pay back on your bills. But because your bills are reduced (the boiler is more efficient) it doesn't cost anything extra, and less when you've paid it off.

[meow2222]

mped CH to a fully pumped system, according to the instruction manual I can use tappings to give me flow across the boiler or either side.

on the left, I could take flow from the top right hand side as the distrib ution tube is on this side or would it be more efficient to take the flow f rom the left hand top or would it make no difference.

For max heat extraction, feed return water in at the top and take water out at the bottom. it gets you cross-flow.

NT

[John Rumm]

If you take your typical fully pumped "Y Plan" layout:

or

You will note that pin 8 on the terminal block feeds both the call for heat signal to the boiler, and also powers the pump at the same time. Hence when the stat is satisfied, the power is cut to both the boiler and the pump at the same time. This basically leaves the mass of the boiler plus the couple of gallons of water it holds sat there "hot" and doing nothing... all that heat will then waft out of the flue.

If you introduce a run on timer (like the kind of thing that keeps an extractor fan running after the light goes out) to continue providing power to just the pump for a couple of minutes after the stat is satisfied, you will get a chance to dump most of that residual heat into the house rather than waste it.

[Roger Mills]

Yes, that would be worth doing. I don't think he's said how he plans to control the system when converting it to fully pumped. Under most circumstances I would advocate going to an S-Plan system with two 2-port valves rather than one 3-port but, in this case, a Y-Plan system may be better.

[Trevor Smith]

I will be using the S plan which will make a pump overrun a bit tricky as I would have to wire it to keep the valve open as well.

[fred]

In article , Trevor Smith writes

It is a little tricky but it can be done.

My choice would be to use a pipe stat rather than a timer, you can set it to run the pump (and open the zone valve) any time there is still warm water in the pipe.

The solution I have in mind would involve a couple relays and a little interconnect. Let me know if you're interested and I will sketch it out.