DIY Doctor

Central Heating Flow Issues With Open Vented System

Postby Deano8 » Sat Dec 07, 2019 11:21 am

Hi all, wonder if you could give some advise. To cut a long story short. I have problems getting any radiators warm. I have an open vented system. Hot water works fine, 3 way valve works fine, new pump fitted but pipe to heating from 3 way valve only gets hot for about a metre and thermostats is new. Pipe is 15mm so I think my whole heating circuit is 15mm, I have tried powerflushing but still no joy. I'm confident no air is in system and feed pipe can't be blocked as I ran with hose on bleed valve and water flow was fine. The only thing I can assume now is that the 15mm piping system is blocked, do you think this is the right conclusion? Time to renew piping? Thanks all
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Postby ericmark » Mon Dec 09, 2019 2:01 am

When bleeding turn off the lock shield and TRV in turn so you bleed both feed and return.
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Postby Deano8 » Mon Dec 09, 2019 6:20 pm

Thanks Ericmark, I've given that a try today. I could feel warm water come up return pipe and warm water up flow pipe when I switched. I'm getting a good flow of water out of Bleed nipple on both flow and return but when I shut bleed back up heat disappears again. So confused.
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Postby ericmark » Tue Dec 10, 2019 5:50 pm

Default is domestic hot water, and it will work to an extent thermo syphon and the boiler is actually switched on by the tank thermostat, so there port valve does nothing in hot water mode.

Quick test is to move the bleed lever and latch it on, often that can temp keep things running, most likely fault is the micro switches in the three port valve.
ericmark
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