Pump and m/valves on return

[eagleeye]

New Vaillant heat only boiler install to replace old Kingfisher floor standing gravity hot water / pumped heating boiler. Boiler on ground floor and dual elson tank in loft.

So the new boiler has gone in the position of the old boiler with also with the pump, m/valves and wiring centre.

They have disconnected and removed the hot water part of the elson and fitted an indirect combi cylinder. left the cold part of elson doing the cold to bathrooms.

Fitted a platform above new cylinder and fitted an f + e tank on that with the feed and vent connected to the flow of the cylinder coil.

I've gone there to wire it all up and found what a mess it is.

My question is this, is the pump and m/valves meant to go on the flow out the boiler and have the feed and vent connected right next to the pump ?

The way its done im sure is drawing air into the system which is causing the issues with the upstairs rads.

Also wouldn't it have been better to fit a system boiler in the first place ?

Now they have this boiler, pump and valves, would it be better to change to the flow and then fit a vessel and filling loop in loft to seal the system

 

[SJB060685]

Ideally it should go vent, cold fill and pump, with the V and C within 150mm of each other, this creates both in the neutral part of the system, a slight negative pressure between C and pump and then a positive pressure throughout the system.
The problem with the pump on return is if the radiator circuit has a higher pressure drop than boiler (almost certain in your case) then water will circulate through boiler and up over the vent, drawing in air each time, as you know this will cause sludge and corrosion over time.
This can be avoided by running the cold fill down to tee in after the pump and before the boiler, this will place the system under a negative pressure and pull the water around hopefully avoiding venting over. Doing this works, however if you have leaky gland nuts or rad valves etc then air can be drawn in that way as well, so like I said works but not desirable.
The other option is like you say to seal the system.

 

[moonlight]

Valves and pump on flow, filter on return.

 

[Chalked]

Weirdly, on that boiler the pump works better on the return.

 

[moonlight]

I fit my pump on the flow, and filter on the return no point having the filter on the flow. Rubbish gone through boiler before it gets there. Valves should be on the flow. Can't tell exactly what is what as can't see connections on top of boiler. I fit Vaillant boilers and heat only ones two.

 

[eagleeye]

Weirdly, on that boiler the pump works better on the return.

So why does it say in the manufactures instructions that the pump has to go on the flow ??
[automerge]1580155572[/automerge]

I fit my pump on the flow, and filter on the return no point having the filter on the flow. Rubbish gone through boiler before it gets there. Valves should be on the flow. Can't tell exactly what is what as can't see connections on top of boiler. I fit Vaillant boilers and heat only ones two.

Valves, pump and magnet are all on the return.

 

[SJB060685]

So why does it say in the manufactures instructions that the pump has to go on the flow ??
[automerge]1580155572[/automerge]

Valves, pump and magnet are all on the return.

Magnet on return yes, 2 port valves can go on return, have seen it done many times and the pump can go on return providing the system is piped properly mate.

 

[Chalked]

So why does it say in the manufactures instructions that the pump has to go on the flow ??
[automerge]1580155572[/automerge]
your correct. But tho open vent vaillant boilers really struggle with the pump on the flow and remote from the boiler.
i always fit the pump next to these, on the return and it works very well.
don't get me wrong, I always fit the pup on the flow, with any other boiler.
have a look at every system boiler and combi, you will see the pump is on the return.

 

[moonlight]

Vaillant boilers have flow sensors