What size boiler needed

[John.g]

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.

 

[sherylryan]

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.

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.

 

[John.g]

Can you point out exactly where this PRV (that's lifting ) is located? Also it appears that there is one EV on the CH system, the 12L one?.

 

[sherylryan]

Can you point out exactly where this PRV (that's lifting ) is located? Also it appears that there is one EV on the CH system, the 12L one?.

Yes there is only the one 12L EV on system . Should this be connected to the pump?

 

[John.g]

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?.

 

[sherylryan]

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?.

Yes the pressure is changing with cold/hot system only slightly though.

 

[John.g]

OK then, suggest noting that pressure the next time the PRV lifts.

 

[sherylryan]

OK then, suggest noting that pressure the next time the PRV lifts.

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.

 

[sherylryan]

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. View attachment 76721

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?

 

[ShaunCorbs]

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.

It’s connected to the return ?

 

[John.g]

If you are referring to the 18L (white) EV, it appears to be connected to the Cylinder cold water inlet? (with blue isol valve), post #87.

 

[John.g]

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?

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. View attachment 76721

Will reply to manifold pump later.

Re boiler external pump, if the EV is connected into the suction side of the pump, the pump discharge pressure should be the EV pressure+the pump head, in your case, 1.3bar+1.35bar=2.65bar, if the EV is connected at the pump discharge then the pump discharge pressure will be the same as the EV pressure, in your case. 1.3bar, the pump suction should then be the EV pressure-the pump head, 1.3bar-1.35bar=minus 0.05bar or minus 0.5M which means part of the system can be running under negative pressure, not desirable as air can be drawn in, in practice boilers (especially Gas) often have their EVs connected into the discharge side but with a EV pressure of 1.3bar and a pump head of say 0.7bar will still result in a positive pressure at the suction side, 1.3bar-0.7bar=0.7bar or 7M.

 

[ShaunCorbs]

If you are referring to the 18L (white) EV, it appears to be connected to the Cylinder cold water inlet? (with blue isol valve), post #87.

Yes not cold inlet coil, cold is below

 

[sherylryan]

Will reply to manifold pump later.

Re boiler external pump, if the EV is connected into the suction side of the pump, the pump discharge pressure should be the EV pressure+the pump head, in your case, 1.3bar+1.35bar=2.65bar, if the EV is connected at the pump discharge then the pump discharge pressure will be the same as the EV pressure, in your case. 1.3bar, the pump suction should then be the EV pressure-the pump head, 1.3bar-1.35bar=minus 0.05bar or minus 0.5M which means part of the system can be running under negative pressure, not desirable as air can be drawn in, in practice boilers (especially Gas) often have their EVs connected into the discharge side but with a EV pressure of 1.3bar and a pump head of say 0.7bar will still result in a positive pressure at the suction side, 1.3bar-0.7bar=0.7bar or 7M.

The EV connects into the firebox, I guess you would say its on the suction side the pump? is 2.65 bar discharge not to high?

 

[John.g]

Its may cause erratic operation of the UFH manifold TMV because you have hot water at high pressure on one side of the TMV and much lower pressure on the other side coming from the cold manifold return.