Exactly as I thought, however the pump needs to be connected (electrically) to the boiler due to the overrun function. Getting a connection up there is going to mean a lot of upheaval with regards to running the cable. Unless I can run a cable externally up the side of the house? Is that possible, or are there rags that prevent this?
Pump in wrong place on Open Vent system...
- Thread starter littlepigeon
- Start date
The photo doesn't give the whole story, a sketch of the complete system would be better.
You say the vent is in the loft, obviously that's where the outlet into the F/E tank is, but the pipe must be tee'd off somewhere, maybe that point isn't quite as remote.
Is the cold fill on the boiler return? For an old system it probably is. If so, I think you'd be OK repositioning the pump to the return, between the cold fill point and the boiler. With pumped return the open vent would normally be between cold fill and pump, but yours would be OK. Some say it's better to have the boiler on the return, as it runs cooler there so should last longer.
On the question of pump over-run - it's a requirement for some modern boilers but I doubt one of your vintage needs it. I have a 20-year old heat-only condensing boiler which doesn't have it.
There's not much more to show in a sketch, but I have added some extra info in this one which may help. I'm not sure what you mean by the cold feed being teed off somewhere? The cold water feed that comes from the tank, is shown in the sketch and the picture. Its a 22mm pipe dropping from the tank and heads towards the central heating two port valve. If that valve is shut, there is a 15mm pipe that links that feed back round to the 22mm pipe coming out of the bottom of the cylinder, which fffrom my workings is what heads back to the boiler (return). The flow pipe from the boiler which heads to the vent splits off and joins the cold feed from the tank (where red meets blue before the vent in the sketch)
I think i may have answered this question above... if not let me know.
My boiler isn't that old, it was replaced about 9 years ago. Its an A rated condensing boiler. Its an Alpha CD24R
Let me know if you need any further info.
Cheers
Having thought about this a bit more - using some typical headloss figures, which of course might not be right for your system, I estimate the pressure rise at the vent point about 1m. In other words, there will be over-pumping if the top of the loop is less than 1m above F/E tank water level. And it's the same whether the pump is repositioned or not. So unless you're prepared to relocate the vent tee, I think your best plan is to just raise the loop to say 1.5m. If you do that you will have to cut the pipe, and it might be worth attaching a length of transparent plastic hose as a test, to see how high the water rises when the pump starts. That way you have something definite to go on.
What is overpumping? Water coming out of the vent? I'm 99.9 percent sure this isn't happening as I've sat and watched and not seen anything come out the vent, but something is getting up the cold feed as it glugs every now and again and the water is warm to the touch (someone has said this can be normal though) Anyway whether it is air or water, it shouldn't be heading up that way should it?
Can you comment on that small 15mm pipe that's feeding the water cylinder coil? Is that right? Surely that would be a bit of a bottle neck when the system is on hot water only with everything else being 22mm. Or is this normal too?
Cheers
OK sorry, I was reading into it something that wasn't there! Warm water in the F/E tank is often a sign of overpumping. Though if it was severe it would be rather more than warm. The cold feed should be Eddie Waring style (if you're young enough to remember him!) i.e. up and under, this minimises convection up the feed pipe, which results in warm F/E tank.What is overpumping? Water coming out of the vent? I'm 99.9 percent sure this isn't happening as I've sat and watched and not seen anything come out the vent, but something is getting up the cold feed as it glugs every now and again and the water is warm to the touch (someone has said this can be normal though) Anyway whether it is air or water, it shouldn't be heading up that way should it?
Can you comment on that small 15mm pipe that's feeding the water cylinder coil? Is that right? Surely that would be a bit of a bottle neck when the system is on hot water only with everything else being 22mm. Or is this normal too?
Cheers
If you're not getting overpumping I haven't much idea about the glugging. Inward air leaks would cause it, but that seems unlikely, there shouldn't be any negative pressure points. Not sure moving the pump to the loft would improve things. Has the problem just started, or have you recently moved in or what?
When you said it's an old system I assumed that included the boiler. I couldn't see anything about pump run-on in the manual, but the boiler needs a permanent live supply, and the pump is powered via the boiler, so it probably has it. But it isn't an issue if the pump stays close to the boiler.
If I think of anything else I'll post!
These are the areas of the manual that I've read that is giving me the ideas things need changing, and that the pump needs to be connected to the boiler..... however i have 2 2 port valvs rather than a single 3 port.
H
Hot&Cold
Yes
have you got the integral 2 channel programmer fitted ?
looking at the latest supplied information,info helps
. A repair to prevent gurgling/boiling over warming the plastic expansion tank needs to be sought.Alterations should include wiring the pump to the boiler,fitting a system bypass,converting to sealed system,ensure the radiators actually need the full boiler output and anything else following onsite investigation.
straight forward repair to bring it up to how it should have been installed
Hopefully the boiler or the system is not already damaged 
That's the bit I was looking at, it shows the pump powered from the boiler, so can give a timed overrun when the live heat demand input ends. If the pump isn't currently connected like that, it should be. I doubt whether it would cure the main problem though.
But I don't fully understand the circuit diagram. I assume that when the external controls call for heat, 240V is applied to terminal 1, the boiler fires and the pump runs. But where does the 240V out from 2 or from 1 via the link, go to, and why?
The diagram doesn't distinguish between a 3-port or 2 two-port valves, but it doesn't need to. The controls tell the boiler to fire and the pump to run when needed, and the valves determine whether it's for HW, CH, or both. Depending on the type of 2-port you have, each most likely has an auxiliary switch inside. The switches close when the valve is fully open, and are connected in parallel, to tell the boiler to fire when one or both switches is closed. This is to avoid the boiler firing with both valves closed, as could happen if it were fired directly, and the valves failed closed.
But I assume the valves are wired up correctly, along with a progammer if any, and that part of it is working OK.
H
Hot&Cold
The link is removed. Terminal 2 supplies electric to the programmer switches,then any thermostat switches,then which ever motorised valve arrangement is fitted. When a successful call for heat is received through all those items then it becomes a switch live and returns to the boiler to power terminal 1.Most uk installers just remove the link and supply their switch live to terminal 1.
that boiler is used in many countries so there are wiring can be varied to suit each country.
Alpha also supplied many boilers with an attached 240v mains fly lead,thats another
issue
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Thanks, the manual didn't make it too clear. Not to me anyhow. Apart from feeding the pump from the boiler, I don't think it's an issue for the OP, as the system is already working.
Most uk installers just remove the link and supply their switch live to terminal 1.
that boiler is used in many countries so there are wiring can be varied to suit each country.
Alpha also supplied many boilers with an attached 240v mains fly lead, that's another
Just to answer this point - it's the vent being tee'd off a pipe I was talking about, not the cold feed. If on your sketch you follow the pipe down from the vent above the F/E tank, the tee is the first junction you come to. I assume that point isn't in the loft.
Incidentally, if your sketch shows how it is physically, I wouldn't do it like that, as the circulating flow can shoot straight up to the vent, and exacerbate the risk of pump over. Better to tee off a horizontal pipe.
I missed some of your other questions, I'll try to come back on them later.
I estimated it from my system, before I'd seen the data for the Alpha CD24R.How did you work that out ? and its normally called pump over.
Flow 1.15m3/h, for 11°C rise at 15kW. Boiler loss 1m, estimated loss for rest of system 1.5m (30m 22mm pipe + some rad entry and exit losses), so pump pressure rise 2.5m. Assumed 10m pipe from pump to vent tee = 0.5m loss. Then taking level datum 0m at the boiler return connection, as is with pumped flow pressures relative to same datum are
at boiler return 0m
at boiler flow and pump inlet -1m
at pump discharge +1.5m
at vent tee +1m
If the pump is repositioned to boiler return, it becomes
at pump inlet 0m
at pump discharge and boiler return +2.5mm
at boiler flow +1.5m
at vent tee +1m
As I said, it's only a rough estimate and may not be too close for OP's system. In fact it can't be if he has the usual 0.45m vent loop height, or there'd be pump over.
The 15mm pipe could be a bypass, to avoid a boiler no-flow condition. Does it have a valve, manual or auto? Some bypass valves are automatic, and only bypass when necessary because everything else is closed e.g. if all the rads have TRVs and they all close. Is the pipework to/from the cylinder coil 22mm? I don't think the 15mm pipe would cause a problem, your glug or otherwise!
Has this problem only arisen recently?