Ecotec plus 630 auto bypass valve issue

[goldman1804]

Hi,

I have an Ecotec plus 630 system boiler which was installed a few months ago, wit a hot water tank and 2 zones (one controlling UFH and the other about 15 rads).

Everything was working fine until a few days ago. As long as both the UFH and the CH zone are calling for heat then the system seems to work fine. However when just the radiators are calling for heat, then the return pipe to the boiler stays cold and only 2/3 radiators warm up. The return pipe just before the boiler (where i have fitted a temp probe) stays at ~25 degrees, but on the boiler in the diagnostics menu it is showing a return temp of ~60 degrees. I can only assume that the bypass is opening and the water is just circling around the boiler.

Any ideas about what's going on / why this may be happening now? I have bled all the radiators and topped the water back up.

Thanks

 

[Johntheo5]

What is the return temp d041? & your measured return temp showing on Ufh only and then with UFH and CH on together?
Also d.040, boiler flowtemp in both cases.

 

[goldman1804]

Thanks for your reply.

In order of flow, boiler return and measured return I get:

CH only: 72, 53, 30
UF only: 63, 43, 41
CH & UF: 67, 47, 44

So as you can see there is a big difference between measured return and boiler return on CH only. This morning it was even wider...more like 70,65,28 with just the CH on. For whatever reason the bypass seems to be open with just the CH, but not when the UF is also on. With a measured return of 30 degrees most of the downstairs radiators don't even get warm.

I don't understand why the bypass is opening (why would the pressure be higher in just CH than in both??). Also the strange thing is that this wasn't happening a few months ago.

Thanks

 

[Johntheo5]

Do you have a system boiler with internal pump or heat only with external pump?. Have you got a low loss header with separate pumps on the secondary side for the CH and the UFH and does the UFH have its own manifold pump, what is the UFH manifold flow temp?.
How many rads and how many UFH Loops.
Is the CH zone valve opening fully.

I see you have a 630 so a system boiler.

 

[goldman1804]

Yes a system boiler with an internal pump.

Not sure if the CH zone valve is opening fully....is there an easy way to test this? It is def letting some water through and i don't seem to manually be able to open it any further when it is "on".
UFH manifold flow temp is set to a max of 50 (but we have weather compensation so usually all runs at a lower temp).
14 rads (a few currently off) and 4 towel rails.
6 loops on the UFH.
No low loss header (as far as im aware)

Cheers

 

[Johntheo5]

Turn off the CH, then pull the lever on the side or end of the motorized valve until you can latch it in, you should feel a fairly stiff resistance while pulling it across, you could remove the actuator, turn the CH on (to fire the boiler) and open the valve manually with a adjustable spanner or such.
Its surprising, the difference between the boiler flotemp at 72C with the CH on and only 63C with the UFH on, the 6 loops might only be emitting ~ 5/6kw so the boiler may be cycling on/off fairly rapidly and not getting the boiler temp up to its setpoint.

The default setting of the internal bypass is set by default very low IMO at 2.5M, I wouldn't mess around with it just yet, the pump speed also has to be set to 100% if you increase it to its max of 3.5M.

Is there any external ABV installed anywhere and if what is it set to?

 

[goldman1804]

So the difference between the flow temp with CH and UF is due to the weather compensation and each being set on a different curve.

Forcing the motorized valve open has made a big difference though! Boiler is no longer immediately dropping to min modulation and is firing fully meaning I can feel all the radiators getting warm. Now we are looking at a CH only of: 70, 55, 49. Still a bit of difference between the boiler return and my measurement, but way closer and everything seems to be working better.

I still don't understand why there is any difference as would have thought it is more efficient to not have any water flowing through the bypass

Thanks very much for your help, wouldn't have thought those valves can fail easily

Thanks

 

[Johntheo5]

That's good but strange allright why the ABV is bypassing on CH but not on UFH, assuming a loop flow of 2LPM and a dT of 8C then the UFH would be emitting 6.7 say 7kw with a flowrate of 12.54LPM @ 49/41C flow/return, returning 7.98LPM @ 41C to the TMV which means the required boiler flowrate is only 4.56LPM @ 63/41C boiler flow/return, the CH, assuming even only 15kw demand with a dT of 20C should be circulating ~ 11 LPM??.

 

[Johntheo5]

Now we are looking at a CH only of: 70, 55, 49. Still a bit of difference between the boiler return and my measurement, but way closer and everything seems to be working better.

Thanks

Assuming the rad output at 15kw, the flowrate is 10.24LPM @ 70C/49C with no bypass, the flowrate is 14.33LPM @ 70C/55C with a fairly hefty bypass of 4.1LPM @ 70C, strange.

 

[goldman1804]

Yes it is still weird, no ideas why it might be bypassing a little bit? It could also be a measurement error accounting for a few degrees?

If you screw in the bypass valve, making it require a higher pressure to trigger (not that i'm going to, just out of interest), then why do you need to set the pump to 100%?

Thanks

 

[Johntheo5]

The pump pumps the water through the Hx (heat exchanger) and then off to the boiler flow pipe, the by pass IMO should be installed after the Hx, but looking at the unclear schematic makes no sense to me as it looks as if it might be installed before the Hx, you might be able to check this on your model.

I see your point re having to increase the speed as it actually makes the bypassing worse with reduced flow, if the pump is at its default setting of 70% and the bypass is set to 3.5M then the by pass shouldnt begin to open until the flowrate reduces to 880LPH , 14.7LPM but if set to 100% speed then it will start to open when the flowrate reduces to 1000LPH, 16.7LPH, these settings seem a bit rediculous to me as a head of 3.5M even after a Hx is regularly required for even modest systems of even 6 to 8 rads.,
By pass shouldnt be required until flowrates fall to < 400LPM, 6.7LPM or even less IMO.
You might have a look at your d settingsre pump speed

 

[goldman1804]

Interesting thanks!

So the pump speed is set to auto which nearly always defaults to 15% unless the boiler is just starting up and the return is really cold (and so the full 30Kwh). At which point I have seen it go as high as 75%.

What are the downsides of making the bypass harder to trigger but not changing the pump speed and leaving it on auto? The manual seems to advise against this.

Thanks

 

[Johntheo5]

I don't really know what 15% refers to, it may be that 0 to 100% range is 53% to 100%, so 15% request may be a pump request of 60% and if the request falls to 0% then the pump request is 53%?? which means the bypass when set to 3.5M will commence opening at ~ 450LPH, 7.5LPM, which IMO is perfectly adequate.

 

[Johntheo5]

I looked up the ecotec plus 430 and it gives the pressure loss through the Hx which almost certainly will be the same for the 630 so can see what these curves really mean.
The Hx head loss is 2.55M at 1290LPH so requires the equivalent of a 4M pump curve so should be just about ok to increase the bypass to 3.5m because once the flowrate fall to 450LPH then the Hx head loss is only, 2.55*sq(450/1290), 0.31M, leaving ~ 3.7M.