You need a 25 l expansion vessel or the next size up eg 35l depending on what you have you can add to it
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What size boiler needed
- Thread starter sherylryan
- Start date
12 Litre
Hi Shaun, yes that's what i was thinking.
Tonight I found a document in our plumbers manual and it states that they are using the DHW expansion vessel, I can't see how this will work as it is 10m away from the boiler on the discharge side of the pump and on the return pipe at the bottom of the cylinder.
And what is the capacity of this one ?
It’s 10 litres. I’m not entirely sure how this would work as the flow for bother ufh manifold goes through the those valves you can see in pic, but there return pipes are 5 metres away from that. The return pipe in the pic (at the top) is for Dhw only.
Yes it is John.
But all of the returns are connected tbh I would say your on the limit of expansion
Are there service valves on them so you could drain and check the pressure one of them might be low / flat
Is the 12L installed in the boiler or outside it and if so is it connected to the boiler circ pump suction side or discharge side?.
Even the 12L on its own if properly charged, per firebird, precharge and fill pressures of 1bar then that alone would only mean a final pressure of 1.97bar with system contents of 214L and 2.23bar with 250L.
Even the 12L on its own if properly charged, per firebird, precharge and fill pressures of 1bar then that alone would only mean a final pressure of 1.97bar with system contents of 214L and 2.23bar with 250L.
Sorry just checked it and it is 18L pre charged to 1.5 bar.
How does this work being situated here when I thought any additional vessel had to be close to the boiler.
Also how would this work with the radiators when there flow is in the completely opposite direction .
It’s on the inside of boiler, but pump is on the outside. It has a hose running from vessel to firebox. Hope that makes sense.
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Does the pressure gauge show 3bar with PRV lifting and what pressure is it showing when system up to temperature?.
You will see a plastic cap (like your car tyre valve cap) just in front of the EV flexible hose, just unscrew/remove (the plastic cap) and depress the needle valve briefly with your finger nail or if not with a small screwdriver and see what comes out.
You will see a plastic cap (like your car tyre valve cap) just in front of the EV flexible hose, just unscrew/remove (the plastic cap) and depress the needle valve briefly with your finger nail or if not with a small screwdriver and see what comes out.
System is on now, showing 1.3 bar on boiler, air comes out of vessel when needle is depressed .
Can on vessel be pre charged to 1 bar and the other to 1.5 bar, do they not have to be the same?
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That other 18L EV has got nothing to do with the heating system, you have a unvented HW cylinder and that 18L EV is to take its expansion, are you sure its not a PRV (expansion valve or main TPRV) from this system that's lifting?.
Its unlikely that the boiler PRV is lifting if the boiler pressure is not exceeding say 2.8/3.0bar.
Even though you have established that the 12L EVs diaphragm hasn't failed the precharge pressure should still be checked as the boiler PRV will lift if this precharge pressure has fallen from 1.0bar to 0.31bar, filling pressure 1.0bar. OR (will lift) if the precharge pressure is correct at 1.0bar but the filling pressure is 1.5bar. So requires system drain down, also the boiler pressure gauge may be faulty, if not and PRV is lifting at < 2.8bar then PRV needs renewing.
Its unlikely that the boiler PRV is lifting if the boiler pressure is not exceeding say 2.8/3.0bar.
Even though you have established that the 12L EVs diaphragm hasn't failed the precharge pressure should still be checked as the boiler PRV will lift if this precharge pressure has fallen from 1.0bar to 0.31bar, filling pressure 1.0bar. OR (will lift) if the precharge pressure is correct at 1.0bar but the filling pressure is 1.5bar. So requires system drain down, also the boiler pressure gauge may be faulty, if not and PRV is lifting at < 2.8bar then PRV needs renewing.
That makes John, I didn’t think the 18L EV had anything to do with the heating system. No the PRV valve on this system goes to a completely different discharge drain.
Would the new pump running at 1.35 bar but was at 2.1 bar cause problem, in the below clip out of instruction manual they talk at static head.
Also attached you will see systems description and the plumber gave us he clearly makes reference to the 18L EV being part of the heating system.
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Yes there is only the one 12L EV on system . Should this be connected to the pump?
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OK, thanks, I see that's a TPRV, normally, what I've seen is just the 3 bar PRV with the over temp protection done with the boiler thermostat at 110 to 113C.
So if this TPRV valve lifts with boiler pressure < a indicated 2.8bar, either a faulty TPRV or improperly charged/filled EV and the pressure is exceeding 2.8/3bar. Presume pressure indication is changing with system cold/hot?.
So if this TPRV valve lifts with boiler pressure < a indicated 2.8bar, either a faulty TPRV or improperly charged/filled EV and the pressure is exceeding 2.8/3bar. Presume pressure indication is changing with system cold/hot?.
Yes the pressure is changing with cold/hot system only slightly though.
Ok will do thanks John. You said in a previous post the boiler pump is normally around .4 bar, 4m head, if this external pump is set to 1.35 bar 13.5m head is this an issue with the expansion vessel, as the expansion vessel charged to one bar allows the system a static head of 5m.
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Another question, I have watched the pump running on both the kitchen (troubled) and laundry manifolds, individually. Correct me if I’m wrong but should the kitchen manifold not run at less RPM than the laundry manifold that had 50m flow and return pipe? The kitchen manifold runs in 32mm cooper from boiler (5m) until it tees off for manifold then it runs in composite 26mm for 2 metres till it joins manifold.
Doesn’t the boiler pump only control the flow and return from the manifold and the manifold pump controls the flow and return in the manifold circuits?
It’s connected to the return ?
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