Vaillant Ecotec Plus 428 with UPS2 Pump

[ChrisNason]

Do they work together?

Part of sorting out the flow in my system was the fitting of a new pump. (The poor power flush filled the old one with iron filings but did cure the boiler noise). So I have a UPS2 which has the 'Variable Speed Mode'. The system is a conventional with loft supply tank and hot water cylinder.

If I use it on Fixed Speed 2 it works just like the old pump and makes noticeable noise when the call for heat is cancelled and it tries to send all its flow through the bypass valve.

If I use it on Variable Speed 3 everything is super quiet. But it doesn't heat the house very quickly. I've just done a test with the boiler set to 65c. The boiler fires as normal but then settles at 36c and almost no noise and the flame symbol still showing. After 5 minutes it gets to 38c. After 10 minutes it gets to 40c.

The flame symbol is showing all the time but I have to get my ear right up to the boiler to hear anything.

Is the UPS2 on Variable not suitable?

 

[ScottishGasMan]

Not really. Variable speed pumps aren't really much use on heat only boilers in general. The boiler modulates the gas use depending on the flow temperature, and can go into a low fire mode if the flow/return temperature spread is too much (as in low water flow through the boiler)

To add, an auto-bypass wont be guaranteed to open when its needed if the pump is altering speed. Its ok in combis/system boilers where the boiler knows and controls the pump speed. on the system you have make sure its kept at a constant speed

 

[ChrisNason]

'Low Fire Mode' sounds like the experience I'm getting.

I upped the boiler temperature to 70c and observed this. After the boiler fired it ran at probably max for 35 seconds and got to 60c before running very quietly. The flame symbol was on as it reduced down to 40c. Then with the flame symbol still on it gradually increased the temperature to 46c up to the 11 minute point. Then it finally went to full power for 5.5 minutes and gradually increased the temperature to 70c.

So for the first 11 minutes it was on this low rate and then turned back to a normal boiler from 11 minutes onwards.

The other feature of my house is the hot water system. The boiler sits directly over the hot tank so the pipe run is probably only 2 metres before it returns. This makes the boiler hit the 70c setting in 15 seconds so it is continually cycling. I thought the variable speed pump would help this?

 

[ScottishGasMan]

The distance to the water tank makes very little difference, its the water flow rate through the boiler thats key.

Is it an unvented cylinder or an older style cylinder?

The only way to correctly reduce cycling is to increase the flow rate through the boiler to the minimum required for the boiler.

The other option that can help is to lower the power output of the boiler to suit the system better. How many radiators are you trying to heat?

 

[ChrisNason]

Eight radiators and it's S Plan Vented Cylinder (fairly new and well insulated).

I tried it on Fixed Speed 3 but the pump noise is heard in the hall below. I've just reduced D0 to 12 (it was on 15) and set the fixed speed to position 2. I've left the target temperature at 70c.

During the earlier test all radiators were coming on at the same time so the balance seems good. The furthest is fully open but I suppose the closer ones may be set too restricted?

 

[Gasguru]

What's the bypass set to?

 

[ChrisNason]

Honeywell bypass set to position 4

 

[Gasguru]

Try setting it much lower..even down to 1 and keep the pump at 2 or even 3. That boiler needs a lot of water circulating through it to keep the sensors and software happy.

 

[ChrisNason]

I set it at 4 because it starts flowing almost as soon as the boiler fires up. I thought it was better to have it only opening when the valves shut down. If I open it won't the hot water just go back to the boiler quicker and shut it down?

I was hoping that the variable speed pump would mean less pressure on the bypass.

 

[Gasguru]

Thats the whole point...have a look in the manual and it will state a minimum flowrate and to achieve that the bypass will need to be open somewhat. At 4 meters water head the bypass will remain closed until both zone valves are shut.
You want a nice 15 to 20 degree temperature drop across the boiler.
Forget the variable pump settings...they dont apply here especially with an over sensitive cupcake boiler that the ecotec 4 series is.

 

[ChrisNason]

I'll measure the temperature drop with my meter but this afternoon it didn't seem to be much different on flow and return. The bypass is flowing with both Heating and DHW in use. If the heated water is going straight back to the boiler won't I have colder radiators and a boiler that is shutting down as soon as it fires?

I'll report back on the temperatures.

 

[fezster]

The recommendation is that a variable speed pump should be used with a fixed bypass:

http://www.newtonnet.co.uk/permanent/GrundfosDocs/BypassCommissioningAlpha2or2L.pdf

 

[picasso]

On this boiler I would be looking to I stall close coupled tees and another pump.

 

[ChrisNason]

The recommendation is that a variable speed pump should be used with a fixed bypass:

http://www.newtonnet.co.uk/permanent/GrundfosDocs/BypassCommissioningAlpha2or2L.pdf

Interesting thought!

 

[Gasguru]

Yes it's all a bit of a mess just to save a few pennies...of course that article doesn't really equate to the real problems of flawed boiler designs such as the 4 series ecotecs and equivalents...over sensitive software, negligible thermal mass, very prone to blockage etc.