Pump overrun

16 Aug 2007
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Newcastle upon Tyne
United Kingdom
I'm thinking of zoning my heating system and have a Viessmann 200-W boiler. One option would be to site the motorised valves close to the boiler (and the control unit) but the potential downside to this appears to be the potential to close off all of the rads and have no where for the heat to go when the boiler is on pump overrun. So, two questions:

I) if all of the rads are shut off have I got a problem?
II) should I consider locating one of the motorised valves after a radiator to enable heat to be circulated through it when on overrun?

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Thanks for that.

After a bit of reading I checked the Viessmann website and found that it says the boiler is fitted with an automatic bypass (same comment on UK website https://www.plumbnation.co.uk/site/viessmann-vitodens-200-w-35kw-combi-

Would an integral bypass do the job or is a separate one required?

Also, as a slight aside. The guy who fitted my system fitted TRVs to ALL rads. I've always thought this was wrong (especially near the thermostat). Am I right or wrong? If you create zones, what do you do about TRVs? Should rads in rooms where there are thermostats have TRVs removed?

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Yes you should remove the trv head or replace with a lockshield valve on the radiators located by a room thermostat. Otherwise the room thermostat will never be satisfied and will keep the boiler running for the whole times schedule.

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