Issues after moving from conventional to system boiler

Issues after moving from conventional to system boiler

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xyz123

Original Poster:

1,078 posts

144 months

Thursday 8th May
quotequote all
Hi, we had a conventional boiler with cold water tank in loft and a hot water cylinder on Y plan system (3 port valve). It was replaced with system boiler and unvented tank. I have had few issues and am struggling with plumber. New system is on S plan with separate valves for hot water and heating. Boiler is Valliant eco tec 630 (plus??). System is controlled via nest thermostat.

Essentially everytime we put hot water on the heating comes on for radiator . From what I can see the heating valve is still open and thermostat contacts are open. So looks like a pipe issue.

Heating engineer who did the work says he needs to fit some sort of non return valve as the return pipes are same. Does this make any sense at all? We haven't paid the labour fee.

Thanks

Yrag male

43 posts

141 months

Thursday 8th May
quotequote all
When i went from vented to unvented, the upstairs used to come on with the hot water, a non return valve was fitted and the heating has performed as it should.

Gary

xyz123

Original Poster:

1,078 posts

144 months

Thursday 8th May
quotequote all
Thanks for your quick reply.

dhutch

16,467 posts

212 months

Thursday 8th May
quotequote all
Sounds like time for a new plumber!

I am surprised you have (two) external valves with a system boiler, or Viessmann has a single internal diverter valve to send hot water to either the radiators or the unvented tank.

It is in effect a combi boiler, with a very larger external heat exchanger for the hot water, same hydraulic block and diverter etc.

xyz123

Original Poster:

1,078 posts

144 months

Thursday 8th May
quotequote all
dhutch said:
Sounds like time for a new plumber!

I am surprised you have (two) external valves with a system boiler, or Viessmann has a single internal diverter valve to send hot water to either the radiators or the unvented tank.

It is in effect a combi boiler, with a very larger external heat exchanger for the hot water, same hydraulic block and diverter etc.
This maybe stupid but do you mean they have fitted wrong boiler? I don't understand the reference to combi boiler, sorry!

Yrag male

43 posts

141 months

Thursday 8th May
quotequote all
My central heating system is over 50 years old and has had 3 extension added to it, the whole lot is controlled by 2 port valves, 5 in total, i am surprised anything gets warm..

dhutch

16,467 posts

212 months

Thursday 8th May
quotequote all
xyz123 said:
I don't understand the reference to combi boiler, sorry!
A 'system boiler' in very similar in build, typically, to a combi boiler. With a combustion chamber, expansion tank, pump, and diverter valve all in one box. Hence I am surprised you have external valves. Either way the installation is clearly not working, so if the current plumber cant resolve it, I would be looking to withhold final payment and find another plumber!

OutInTheShed

11,441 posts

41 months

Thursday 8th May
quotequote all
Yrag male said:
When i went from vented to unvented, the upstairs used to come on with the hot water, a non return valve was fitted and the heating has performed as it should.

Gary
Could be thermal syphoning from the HW return into the rad system.

The current plumber is not necessarily going to be responsible for the existing pipework, the layout of which can encourage this sort of thing.

An NRV in the heating return close to where the returns join should fix it.

xyz123

Original Poster:

1,078 posts

144 months

Thursday 8th May
quotequote all
Thanks everyone. Plumber fitted NRV in on one of the pipes and it seems to work OK. We have agreed to test it for another day before paying him.