full gravity fed, pumped y-plan system, midposition 3 port valve (3PV), simple potterton 15kw regular boiler with all the usual gubbings (room stat, time clock, cylinder stat) in with the cylinder. 3 story town house, 3 rads top (beds), 5 rads middle (living), 3 rads ground (kitchen). 11 rads in total... all on 10mm pushfit that is on display and i'd image 15/22mm lurking under the floorboards as per.
When in mid position water is scorching and the last two radiators on the loop do not get hot. 3PV is definitely working as the call for heat from both CH and HW is always satified, both together and individually.
I balanced the rads (prev plumber left lockshield fully open... i think we've discussed that before!) and when in CH mode only, the rads heat up fine, it's only when the CH and HW are calling together, the two rads in kitchen go cool/cold.. heating still works for the rest of the house and the hot water is up at about 75/80 degrees at the tap, so my thermometer tells me.
Pump is set to 3 and is working fine, no sludge in system as it is relatively new.
So my question is, any ideas why when in mid position those last two rads go cold? Do you think there could be a problem with the valve itself when in mid setting?
Does the DHW coil have a restrictor / lockshield valve fitted? Is it open too far? If the rads go cool when the valve is in the mid position, it suggests the water is just scooting through the cylinder coil in preference to the heating circuit.
A cylinder coil has a 22mm diameter so will have little resistance so will need to be balanced just as the radiators do and if you have closed down some of the lockshields, then the flow through the coil will have increased.
Htg, put a different pump on, more powerful, same issue, just not getting hot, but the hot water is v hot. The pump is on top floor, there are a few runs of 10mm that I would say are longer than 3meters on both flow & return. this might be the cause of the heartache?
I like the idea of throttling the DHW coil but I have never seen it in practice. That would help with the long runs.
No gatey/lockshield on the DHW coil, are you suggesting that I fit a 22mm one on the return of the coil and throttle it in a similar fashion to my rads?
I suppose in essence it is a very simple concept water flow, surely the original installer (barrat homes) would have thought this through?
You have not seen a valve in the DHW circuit? I am surprised. It's a very long time since I have seen a "S" or "Y" plan WITHOUT one. Fit a 22mm gate valve in the circuit and crack it open about 1 to 1.5 turns.
The cylinder coil is 22mm so if unrestricted will simply act as a bypass and rob the heating circuit pretty much totally when the 3PV is in the mid position.
Obv i'm someone with not as much knowledge as you guys but could you please tell me how this system could a full gravity system i it contains a y-plan and mid position valve. Surely that would make it fully pumped?
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