How to set a bypass valve

[Graham J W]

Hi, can anyone tell me the minimum flow rate for a Valiant ecotech plus 424 boiler. I am trying to set my Honeywell bypass valve. (boiler keeps over heating and going into anti cycle mode). I think it could be lack of flow ?.

Cheers
Graham.

 

[BlueLoo]

What pump do you have

 

[noddy997]

Hi, can anyone tell me the minimum flow rate for a Valiant ecotech plus 424 boiler. I am trying to set my Honeywell bypass valve. (boiler keeps over heating and going into anti cycle mode). I think it could be lack of flow ?.

Cheers
Graham.

If boiler is overheating that's an issue with your pump.

 

[Graham J W]

Hi Noddy997,

New Grundfos UPS3

 

[noddy997]

Hi Noddy997,

New Grundfos UPS3

Still overheating with a new pump? I'm not a fan over those ups 3 personally. Don't really like them

 

[Johntheo5]

Hi Noddy997,

New Grundfos UPS3

What mode/setting is it on?.

 

[Graham J W]

Its a UPS3 set on constant pressure 1.

 

[Johntheo5]

Is the by pass a (angled) Honeywell DU145 and what setting is it on? these angled ABvs for some reason or other give huge bypass flows. Would suggest setting it to index 3.5/3.8.
Is the boiler cycling immediately on firing up or sometime later?.
Can you check these boiler d settings.

 

[Johntheo5]

Should also have asked what is the target flow temperature?, and when/if its running can you check the flow/return temps d.40&d.41.

 

[Graham J W]

Hi Johntheo5

Honeywell straight connection which is set at 4. Boiler is firing up from cold and continues up to running temperature which is set at 62C flow. It seems happy with all TRVs open but temp starts rising beyond the 62 and in anti cycle mode once TRVs start closing. Temp then goes to 66 and into anti cycle mode.
d40 63 d41 53 ish.
I am now also looking at the partial load setting. 24kW boiler but my loading is about 12.5 kW. Tried putting it down to 16kW but it did not like it nor when set in auto. I've put it back to 24kw for now.

 

[BlueLoo]

Its a UPS3 set on constant pressure 1.

Therein lies the problem.
CP is for UFH and doesn't play nice with AVVs.

Either fit a manual bypass (tacosetter) and use PP or use CS.

You'll go round and round in circles unless you set the pump to match the bypass.

 

[Johntheo5]

A flow/return of 63C/53C should result in rad output of 70% of their full T50 rating, assuming 24kw rad output at T50 conditions then the boiler /rad output is now 16.8kw with a flowrate of 24.1LPM
You say the flow temperature starts rising as the trvs start closing, theoretically if they closed to the poind of tripping the boiler due to a high dT flow/return of 30C then you would have seen the return d.41 falling to 35C, 65C/35C, dT 30C still gives a boiler output of 12.35kw but the flowrate is then only 5.9LPM so something strange in that the boiler should still have controlled to its target temperature.
Your ABV will be doing absolutely nothing at a setting of 4 as the UPS3 CP1 setting is a constant 3.0bar, maybe worth looking at this and also note carefully d.41 as the TRVs start throttling in.

 

[Johntheo5]

Therein lies the problem.
CP is for UFH and doesn't play nice with AVVs.

Either fit a manual bypass (tacosetter) and use PP or use CS.

You'll go round and round in circles unless you set the pump to match the bypass.

Yes, even though I have set up one (UPS3) + ABV running on CP1 without a manual bypass, it is better although the UPS3 in effect doesn't have any CS curves, it has 5 CP settings and 2 PP settings, (you should have a look at the UPS2 8M pump), If yo.u look closely at the CS settings there is a very very gradual fall off in head, any "true" centrifugal pump head will start falling as soon as it starts pumping

 

[BlueLoo]

Yes, even though I have set up one (UPS3) + ABV running on CP1 without a manual bypass, it is better although the UPS3 in effect doesn't have any CS curves, it has 5 CP settings and 2 CP settings, (you should have a look at the UPS2 8M pump), If yo.u look closely at the CS settings there is a very very gradual fall off in head, any "true" centrifugal pump head will start falling as soon as it starts pumping

View attachment 325376

There is a good paper by grundfoss on this issue.

It effectively negates the benefits of a PP pump with pressure controlled bypass arrangements.

After fannying around with multiple configurations to see if i could get a pp pump to play nice with a external bypass, i ended up using a NO actuated valve between flow and return (there is a paper from WB on this).

Works perfectly now.

 

[Graham J W]

The pump does seem to be quietThank you BlueLoo and Johntheo5

I am a real novice when it comes to central heating unfortunately so any advice gratefully received. The pump does seem to be quiet powerful to me as some of the TVRs (TRV4s) are noisy with water velocity. I believe from Grundfos data that using PP2 as an option is not a good idea with a ABV. What setting would you suggest for the ABV with the UPS3 on CP1.