How to set a bypass valve

[Johntheo5]

OK, your boiler is recycling because the demand is below the boiler minimum output and when you reopen the TRV then the heat demand increases to = or > than the boiler 6.2kw minimum output, at least for awhile. The circ pump should not stop IMO in recycle, is it stopping before the the anticycle time of ~ 4 minutes has elapsed? . 55C is also far too high to allow the boiler to get away without repeated anticycling.
When the boiler is next running "normally" with its 63C flow temperature, feel the pipe a bit below the ABV, it will/should be cold (at setting 0.45?) then keep turning the adjusting knob slowly anticlockwise while feeling the pipe, as soon as the pipe start getting hot stop the adjustment, it should then be reading ~ 0.25/0.28ish, wait a few minutes and read d.40&d.41, when next it goes into recycle read off d.40&d.41 just before the end of the recycle period and post back.

 

[Graham J W]

Thanks Johntheo5

Will do tomorrow and get back.

 

[Graham J W]

Good evening Johntheo5,

Update.

Firstly I have found out why the pump was cutting out in anti cycle mode activation. Pump overrun was set at 5 minutes and anti cycle 6 minutes.I changed the pump overrun to 8 minutes and that solved that one.

Boiler set to partial load 11 KW. I see that d.085 minimum capacity can be set between 6 KW and 13 KW.

Settings I have found.

d.001 Pump overrun heating 8 minutes.
d.002 Max anti cycle time is 20 minutes.
d.005 Heating target flow temperature 63 C.
d.007 Cylinder target temperature 55 C.
d.020 DHW target temperature 60 C.
d.071 Max heating target flow temperature 75 C.
d.077 DHW partial load 30 KW.
d.085 Minimum capacity 6 KW.

Observations :Start up from cold.

Wall thermostats set at 22
TRVs set at 4.
ABV set at 04.5
Flow temperature set at 63 C
Partial load set at 11 KW
Pump set on CP 1
Pump overrun was still 5 minutes at this stage.

With those settings the burner took 48 minutes to reach set flow temperature. (burner mainly on low)

30 mins Flow 50 return 37
40 mins Flow 58 return 44
45 mins Flow 62 return 47
48 mins Flow 63 return 51
50 mins Flow 64 return 52
52 mins Flow 66 return 53
53 mins Flow 67 return 53
Burner tripped and anti cycle started ( 6 minutes)
Pump stopped at 1 minute remaining.
Pump started after 2 minutes.
Burner fired back up.
Flow and return at end of anti cycle mode was 51 flow 49 return.
The flow quickly raised to 67 C and back into anti cycle.

This is when I found the pump overrun setting of 5 minutes. By adjusting this to 8 minutes it certainly helped reduce both flow and return temperatures. It took the flow temperature down quicker whilst in anti cycle mode. The system settled for a while and in fact the return temperature dropped a lot down to around 37 C.

I tried adjusting the ABV Ie opening it up from 04.5 to 03.5. This increased the return temperature which in turn increased the flow temperature and back into anti cycle. I put it back to 04.5

Conclusion

Return temperatures still fluctuate as ( I think) TRVs open and close but seem less influential on anti cycle. The average is still 40s.
Opening the ABV above 0.45 increases return temperature quickly.
Flow temperature rising looks to be the primary cause of anti cycle.

Again, by opening the large rad TRV in bedroom I to full, it seemed to "suck the heat away from the boiler". Flow temp dropped and the upstairs return temp lowered significantly. Boiler settled for a while until the system caught up with it and eventually into anti cycle.

I think we are of the same mind ?. The system load is to low to absorb the heat produced by the boiler and it is not being dissipated by the rads before returning it.

It feels as thou the boiler is not being allowed to "breath".

What do you think my options are.

Thanks
Graham.

 

[BlueLoo]

Can i ask why you are continuing to think CP is a valid pump mode?

 

[Johntheo5]

Thats certainly comprehensive testing Graham.

I don't think you really have any options if the heating load falls below the boiler minimum load except to ensure as much as you can that the boiler fires up on one attempt after recycle and runs until the flow temperature again trips the burner at 67/68C., that is as good as it gets then as a boiler cycling should really be no big deal, my 18 year old oil fired boiler constantly cycles (since it can't modulate) with no problems.

This bit puzzles me though
Burner tripped and anti cycle started ( 6 minutes)
Pump stopped at 1 minute remaining.
Pump started after 2 minutes.
Burner fired back up.

At a (max) anticycle time of 20 minutes and a target temp of 63C then the anticycle time should, theoretically, be 5.1minutes, say 6 minutes actual max, the pump stopped with 1 minute remaining which "proves" the actual anticycle time of 5.1 minutes, now I wouldnt have thought that the pump would/should then stop and restart after a further 2 minutes but this is possibly normal for a Vaillant, what I can't figure out is why increasing the overrun time from 5 minutes to 8 minutes helped since overrun should not have been requested, are you saying that the "anticycle"time then lasted for 8 minutes?.

What you might consider doing is reducing the overrun time back down to 5 minutes and increasing the (max) anticycle time to 35 minutes to give a actual anticycle time of 8.4 minutes and note again the actal anticycle time and pump stopping/restarting again, it wwoud/will be interesting.

 

[Johntheo5]

Can i ask why you are continuing to think CP is a valid pump mode?

I'll try and reply to this.
Apart from getting a ABV to operate as designed, ie to start opening as the pump head increases on reducing flow rate , radiators can and often are serviced by a pump in CP mode, I have a 10 rad system with a 6M Wilo Yonos Pico pump with 3 CC settings and CP and PP modes that can be incrementally changed in 0.1M steps to give any desired flow rate. I run my pump in a PP 4.7M mode which gives me my required flowrate at a head of 3.5M with all TRVs opened, the pump head then falls as the TRVs throttle down and my kitchen rad, on the end of a very long run is a little slow in getting up to temperature, in very cold weather (very uncommon here) at say < -2C I run the pump in CP mode at 3.6M, the kitchen rad then heats up almost as rapidly as the remainder of the rads. I don't have either a manual or a ABV, oil fired boiler, non required as the 25L boiler HEX soaks up any residual heat. (CC2 on my Wilo gives a reasonable constant curve for setting up a ABV).

The UPS3, IMO, does not have any CC curves, valid or otherwise, one of the few pumps I've come across in the past few years with true CC curves was a DAB Evosta 4-7M, see below, I installed one for a neighbour a good few years ago (rad system) and had no problem whatsoever setting up the DU144, ABV.

 

[BlueLoo]

I'll try and reply to this.
Apart from getting a ABV to operate as designed, ie to start opening as the pump head increases on reducing flow rate , radiators can and often are serviced by a pump in CP mode, I have a 10 rad system with a 6M Wilo Yonos Pico pump with 3 CC settings and CP and PP modes that can be incrementally changed in 0.1M steps to give any desired flow rate. I run my pump in a PP 4.7M mode which gives me my required flowrate at a head of 3.5M with all TRVs opened, the pump head then falls as the TRVs throttle down and my kitchen rad, on the end of a very long run is a little slow in getting up to temperature, in very cold weather (very uncommon here) at say < -2C I run the pump in CP mode at 3.6M, the kitchen rad then heats up almost as rapidly as the remainder of the rads. I don't have either a manual or a ABV, oil fired boiler, non required as the 25L boiler HEX soaks up any residual heat. (CC2 on my Wilo gives a reasonable constant curve for setting up a ABV).

The UPS3, IMO, does not have any CC curves, valid or otherwise, one of the few pumps I've come across in the past few years with true CC curves was a DAB Evosta 4-7M, see below, I installed one for a neighbour a good few years ago (rad system) and had no problem whatsoever setting up the DU144, ABV.




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Detailed answer. Thank you.

CP really demands a low loss system with very little friction losses or delta between emmiters. It is a pressure biased system, not flow and flow is the primary condition we should be worrying about (ignoring knackered plumbing).

I could get away with CP in my system because it's clean and uses distribution and return manifolds and has a electronic actuated bypass.
However, for ABV, the CP is beyond useless because you get xero Delta P. Which the ABV works on.
On older systems without manifolds and variable losses, i don't see how that works in CP mode either and then you have the energy wastage of it.

Ymmv. But moving from a CS pump to a VS pump needs careful system consideration.

In the OPs case, i cannot see how anything other than CS works.

 

[Graham J W]

Grundfos recommend the constant pressure setting for the UPS3 pump on central heating systems fitted with ABVs. Ie fixed speed 1,2 or 3. The pump does have a proportional pressure setting but as they state, only to be used on a system with no ABV.

An option I am considering and Johntheo5 could you advise please as a trial for my issues. I feel that the UPS3 even on CP 1 could be to fast / pressure for my new pipework and rads. Thoughts are, close the ABV and remove the TRV on one of the downstairs rads and balance a constant flow through it. Use this rad ( and the towel rail for upstairs) as heat sinks / pressure release. Set the pump to PP2 ?.

 

[Graham J W]

Grundfos UPS3 pump settings

Grundfos Pump Settings - Heatweb Wiki

www.heatweb.co.uk

 

[Johntheo5]

Grundfos recommend the constant pressure setting for the UPS3 pump on central heating systems fitted with ABVs. Ie fixed speed 1,2 or 3. The pump does have a proportional pressure setting but as they state, only to be used on a system with no ABV.

An option I am considering and Johntheo5 could you advise please as a trial for my issues. I feel that the UPS3 even on CP 1 could be to fast / pressure for my new pipework and rads. Thoughts are, close the ABV and remove the TRV on one of the downstairs rads and balance a constant flow through it. Use this rad ( and the towel rail for upstairs) as heat sinks / pressure release. Set the pump to PP2 ?.

Your new pump is a UPS3 and not a UPM3??

Not sure where you are coming from re above but you can certainly try the above, its only a few button presses.
I reckon that with the TRVs open that you may have a boiler load of ~ 10kw, if so, then a dT of your 14C will require a flowrate of 10.2LPM, when/if you change to PP2 then the result will be a 8.4LPM flow at a head of 2.1M.

 

[BlueLoo]

Grundfos recommend the constant pressure setting for the UPS3 pump on central heating systems fitted with ABVs. Ie fixed speed 1,2 or 3. The pump does have a proportional pressure setting but as they state, only to be used on a system with no ABV.

An option I am considering and Johntheo5 could you advise please as a trial for my issues. I feel that the UPS3 even on CP 1 could be to fast / pressure for my new pipework and rads. Thoughts are, close the ABV and remove the TRV on one of the downstairs rads and balance a constant flow through it. Use this rad ( and the towel rail for upstairs) as heat sinks / pressure release. Set the pump to PP2 ?.

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

They actually don't.
They say "if... must"

It's a fudge solution which they admit isn't ideal for obvious reasons.

The last paragraph is the key. "Use a manual bypass".

 

[Johntheo5]

THe UPS3 doesn't have constant speed modes?.

 

[Graham J W]

Grundfos operating instructions for the UPS3 attached.

Section 6

6.2.1 Refers to the factory setting of Constant curve or Constant speed 1,2 or 3.

6.2.2 * Proportional pressure mode is not recommended in heating systems that include an ABV.

BUT,

I also found this on their website ?.

Radiators

Conversely, radiators with thermostatic radiator valves (TRVs) use the TRV to adjust the flow to the radiator depending on the heat demand. This ensures correct room temperature and optimal comfort for the home owner.
A low heat demand/flow leads to lower pressure losses in pipes and fittings in the heating system, in this case to prevent pump pressure that is too high, resulting in unnecessary energy use as well as risk of noisy valves. The pump should be set to the proportional pressure setting where the differential pressure adjusts proportionally to the required flow in the system.

 

[Johntheo5]

A TRV will work with any pump mode you wish to use. As stated above, if the pump head is too high either in constant curve or constant pressure mode then this may lead to noisy TRV operation and will also lead to unnecessary energy usage. The UPS3 so called CC1 is 4.2M which will waste power as its not required at your flowrates and may lead to noisy TRV operation, its useless used in conjunction with a ABV as it effectively gives a constant pressure (head) of 4.2M up to a flowrate of 12.5LPM, this pump has, to all intents and purposes, 5 CP modes and 2 PP modes.

 

[Graham J W]

I bow to your superior knowledge in these things Johntheo5.

My downstairs heating suffers from terrible TRV noise !. Upstairs far less.

The new downstairs pipe runs are much shorter so flow rate will be higher ??.

Can / should I try another setting on the pump and if so which.

( my inclination when my issues started, was the water had to much force and was "hitting" the TRVs hard and with heat rapidly)