Differential bypass valve

The new Vaillant eco TEK boiler I am fitting during the xmas holiday has pump over-run control from the boiler. The system has three zone control valves and a few rad's with TRV's directly connected to the F & R.

There will be occasions when the pump will be activated by the boiler and there is no path for the water so the first job is fitting a Comap 22mm differential bypass directly between F & R.

The unit is adjustable between 0.1 and 0.5 bar. My problem is that it is not obvious what setting to use. There is no external indication when the thing operates.

Does anyone have advice on how to determine the correct setting? My guess is to keep increasing the pressure until it shuts under normal conditions. Hopefully it will be possible to detect a flow through the valve by temperature change.

Finally, it seems obvious to me that a better solution would be to have the boiler open one of the zone control valves when pump over-run is required. I can see how to do this with relays but is there a more elegant solution?

Merry xmas

Brian

Reply to
Brian Drury
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Dont these boilers have built in auto bypass valves ? Robert

Reply to
robert

You would think so but they don't.

There is are clear instructions in the manual to fit one but no details of how etc.

Brian

Reply to
Brian Drury

That doesn't sound like a very good idea to me! Pump over-run only normally needs to operate for a few seconds to carry away the residual heat from the boiler when it has been shut down because all demands are satisfied. A zone valve will take a finite time to open - by which time it is probably too late, and the boiler will have over-heated and tripped out.

Worse still though - assuming you have an S-Plan (or S-Plan+) system - it is the volt-free contacts in the zone valves (which close when the valve opens) which control the boiler. So if you open a zone valve artificially when it should otherwise be closed, it will turn the boiler back on - and that zone will run continuously and defeat any controlling thermostats.

Reply to
Roger Mills

I used a mid position valve to control my 2 heating zones rather than two zone valves. The main reason for this is there's always a water path.

Reply to
Andrew Gabriel

Sorry, all the sealed system and combi boilers have built in bypass - it seems only the open vent version dont ! I've just fitted the ecotec plus combi and knew it had a built in bypass. Robert

Reply to
robert

Excellent, so you must know how to set it up!

I would appreciate knowing what you did.

Thanks

Brian

Reply to
Brian Drury

My Ecotec plus 837 combi didnt really need any setting up ! Just remember to fill condensate trap with water before firing up for first time !

Robert

Reply to
robert

Thanks for the condensate tip Robert. I should have remembered but I might not have. The instructions do mention it but it could be missed although the checklist reminds you to check you read the instructions!

Presumably you don't have a control on your bypass valve. It is interesing that Vaillant tell me to put my bypass in at least 1.5 metres from the boiler. Dunno how they do that when they fit the bypass inside the combi boiler.

The eco TEC plus 418 is on the wall but not plumbed in. The bypass is now plumbed in and I tried adjusting it with the existing boiler running. It seems that any setting above 0.15 bar the bypass remains shut. This is with an average looking three speed Grundfos pump set to the lowest speed. I think the bypass sometimes 'leaks' a little at 0.1 bar but better that than not opening. I have left it at roughly 0.12 bar.

Google shows up several installation instructions for different makes of bypass but none of them suggest how to determine the optimum setting. There are vague suggestions like adjust bypass according to the system requirements.

You would think that several people on here would know the correct way to set it up. Maybe they have not recovered from yesterday yet.

Curiously the boiler instructions insist that all systems must have at least one radiator not fitted with a TRV! So why the bypass valve?

Anyhow, tomorrow's job is to plumb in the eco TEK. (Must go fill up the condensate trap before I forget)

Brian

Reply to
Brian Drury

The one rad without TRV is heating the area where your thermostat is sited.

On my Ecotec the bypass is not adjustable and the 2 speed pump sorts itself out - (at least on any default settings).

Failure to fill the condensate trap results in combustion fumes coming into the house ! Robert

Reply to
robert

The worst that would happen if you didn't fill the trap is that flue gases would go into the condensate drain and then perhaps somewhere else for about 20 minutes. This is not desirable nor competent practice but frankly not _likely_ a serious problem.

The book on the combis say to set the differential bypass to 0.35 bar. However there is no practical way of measuring this.

I would set the by pass about 1/2 up the scale and then see if it opens during pump overrun.

Reply to
Ed Sirett

Thanks Ed.

You right there is no way fumes will leak if the trap is not filled with water but it says to do it so I did it.

Maybe Robert is collecting the condensate indoors :)

Now the boiler is running it looks as if we have just chosen a new pope. The steam cloud coming from the chimney is quite impresive.

I have found the bypass works best at the lowest setting.

Reply to
Brian Drury

Just for initial testing purposes :) But as the the condensate pipe doesnt have to be a sealed connection all the way to the drain, there is still the potential for fumes to void into house if condensate trap isnt filled . Robert

Reply to
robert

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