Flow rate needed

[jamesdiyer]

I do seem to have two issue. 

 

The exterior temperature sensor seems to have been placed in a microclimate as it's 2C above exterior (real) currently. 

 

Also the DHW is reading 23C as the sensor is quite low down, as on photo. Maybe this needs be higher. Or mains water arrives around 12C. The tank isn't 23C as it's coming out nice and hot. Suggestions on this one and where it should be would be helpful. 

I've set the DHW that it can heat in two windows per day (cheap off peak) so perhaps it's not an issue as it won't be constantly trying to heat. 

 

 

Thanks 

 

 

 

 

Edited Thursday at 17:30 by jamesdiyer

[jamesdiyer]

Also I realise I can reduce the target DHW temp. I should be less worried about temps as actual temps and treat them as a tool to adjust based on if we have enough hot water. 

Edited Thursday at 19:17 by jamesdiyer

[JamesPa]

2 hours ago, jamesdiyer said:

The exterior temperature sensor seems to have been placed in a microclimate as it's 2C above exterior (real) currently. 

This should be located in the shade where the air is free flowing.  If the offset is constant it wont matter much, if its not constant it will and should be relocated.

 

2 hours ago, jamesdiyer said:

Also the DHW is reading 23C as the sensor is quite low down, as on photo. Maybe this needs be higher.

Fairly normal.  DHW manufacturers assume people want something close to a full tank or at least half a tank and locate sensors accordingly.  Putting it at the top would mean that reheat is triggered only when its empty, meaning that there is a period when DHW is unavailable, which the majority of punters will complain about.  Just adjust your schedule/hysterisis to get what you are comfortable with

[jamesdiyer]

The sensor is located near the heat pump in the shade but under a lean too roof, so it's a microclimate. I'll ask the installer to move it to a North wall. 

 

And thanks for confirming the tank situation, makes sense. It is actually a good location thinking about it, it's a 200L tank and some family members like scalding huge baths. 

[jamesdiyer]

Another question. 

 

I noticed the flow return pipe between the 3way valve / volumiser and radiator input is done in 25mm plastic, so 20mm internal. It's about 3m of pipe overall. From A to B. After point B, the copper pipe splits immediately into two 22mm coppers one for upstairs on for down, so it is a restriction. 

 

The pipe between diverter is 32mm external. If on DHW cycle we get 2000l/h but 1700l/h heating circuit. 

 

Could this short stretch of reduced pipe be reducing flow so much? Before I ask installer to change. 

 

 

Edited yesterday at 05:26 by jamesdiyer

[JamesPa]

2 hours ago, jamesdiyer said:

The pipe between diverter is 32mm external. If on DHW cycle we get 2000l/h but 1700l/h heating circuit. 

 

Could this short stretch of reduced pipe be reducing flow so much? Before I ask installer to change

Possibly.  1700l/h is a bit low for 12kW (12000/4200/5*3600)=2000l/h.  I would describe this as sloppy plumbing.

 

Why is what appears to be the sensocomfort in what appears to be the plant room/garage.  This should be in your house so the heat pump knows the OAT and control the heat pump.  Its normally wireless so you can put it somewhere convenient.  Maybe Ive misinterpreted the photo.  I hope you arent using third party controls/thermostats.

Edited yesterday at 07:53 by JamesPa

[jamesdiyer]

27 minutes ago, JamesPa said:

Possibly.  1700l/h is a bit low for 12kW (12000/4200/5*3600)=2000l/h.  I would describe this as sloppy plumbing.

 

Why is what appears to be the sensocomfort in what appears to be the plant room/garage.  This should be in your house so the heat pump knows the OAT and control the heat pump.  Its normally wireless so you can put it somewhere convenient.  Maybe Ive misinterpreted the photo.  I hope you arent using third party controls/thermostats.

 

The sensor comfort is there temporarily, it's wired and I couldn't decide where to put it - walls are 80cm think. I'm running pure weather compensation. 

 

Yes your comment alludes to my first question, I felt 1700l/h is low - and I have a 15kw machine. But others here said running 32mm external 26mm internal plastic pipe over 11m isn't enough bore. 

[JamesPa]

41 minutes ago, jamesdiyer said:

Yes your comment alludes to my first question, I felt 1700l/h is low - and I have a 15kw machine. But others here said running 32mm external 26mm internal plastic pipe over 11m isn't enough bore. 

What the plumber has done with the plastic pipe is just lazy.  It's the 'never time to do it right, always time to do it twice mentality'. 

[jamesdiyer]

8 hours ago, JamesPa said:

What the plumber has done with the plastic pipe is just lazy.  It's the 'never time to do it right, always time to do it twice mentality'. 

 

Yes sadly that's so, and parts on the install weren't discussed with me. 

 

 

 

On another note, my monitor says basic circuit diagram 8. However if I am just with a volumiser and DHW tank, radiators only 1 circuit, should this be 7? 

 

Edited yesterday at 17:12 by jamesdiyer

[marshian]

13 hours ago, jamesdiyer said:

Another question. 

 

I noticed the flow return pipe between the 3way valve / volumiser and radiator input is done in 25mm plastic, so 20mm internal. It's about 3m of pipe overall. From A to B. After point B, the copper pipe splits immediately into two 22mm coppers one for upstairs on for down, so it is a restriction. 

 

The pipe between diverter is 32mm external. If on DHW cycle we get 2000l/h but 1700l/h heating circuit. 

 

Could this short stretch of reduced pipe be reducing flow so much? Before I ask installer to change. 

 

 

 

Just a random thought from me - those valves are full bore ones and not the restrictive types?

[jamesdiyer]

1 hour ago, marshian said:

 

Just a random thought from me - those valves are full bore ones and not the restrictive types?

 

Good question. The red ones yes. The blue ones on the heating pipes should have come out during the install but we're left. They were only placed there so I could pressurise the system prior to installer coming to check some repairing I'd done was fine. So they'll come out when he's back. 

[JamesPa]

1 hour ago, marshian said:

Just a random thought from me - those valves are full bore ones and not the restrictive types?

I think you can guess!, and I fear you will guess correctly!

 

2 hours ago, jamesdiyer said:

On another note, my monitor says basic circuit diagram 8. However if I am just with a volumiser and DHW tank, radiators only 1 circuit, should this be 7? 

 

Not sure what 7 and 8 refer to here.  In my set of schematics from a year ago 

 

7. No modules

8. uniTOWER, Buffer

 

So 7.  Not sure if it actually makes a difference though to the settings, it could, it might, but it might not!

[jamesdiyer]

34 minutes ago, JamesPa said:

I think you can guess!, and I fear you will guess correctly!

 

Not sure what 7 and 8 refer to here.  In my set of schematics from a year ago 

 

7. No modules

8. uniTOWER, Buffer

 

So 7.  Not sure if it actually makes a difference though to the settings, it could, it might, but it might not!

 

Actually looking the part manual they seem to be full bore and they're 1" so 22 internal but will know when off. 

 

If we're talking restrictions, then the plastic 25mm pipe fittings are internal of that. The pipe id is 20 and so you're looking at 15mm inside of the fitting id. But that's a very tiny distance, so I'm not sure it matters? (Everything matters in totality) 

 

Annoyingly vaillant Spain seem to be useless, which isn't good. I got some answers from vaillant UK very easily - flow should be targeted at 2000l/h, and send me their installer handbook with figures. Not surprising. 

[SimonD]

What delta T are you measuring between the flow and return of your heatpump when it is running on CH? 

[jamesdiyer]

2 hours ago, SimonD said:

What delta T are you measuring between the flow and return of your heatpump when it is running on CH? 

Well 5. But the heat demand is very low currently. 

 

I'm not sure how to force the highest heat demand from the hestpump to see what the delta t and max kW produced is.

[SimonD]

1 hour ago, jamesdiyer said:

Well 5. But the heat demand is very low currently. 

 

I'm not sure how to force the highest heat demand from the hestpump to see what the delta t and max kW produced is.

 

In room temp. mode on your controls, what is it configured to? Is it Inactive (so weather compensation only), Active or Expanded? If it's on active or expanded your sensocontrol will be influencing output and modulation of the heatpump together with weather compensation. You might try to adjust your weather comp curve to highest as well as any room temp sensors to get the HP cranking up its output as much as you can.

 

1st you need to go around the whole system to make sure that all valves and actuators are fully open and then make sure that all your radiator valves and any TRVs are also fully open. If you have any TRVs do you also have a bypass valve in the system, or is it just installed fully open loop?

 

Once you know the heatpump is running and all your radiators are getting warm, Now check your flow rate. 

 

If your flow rate is still looking low, then go into your installer menu and into the configuration menu and look at Config CH Build Pump and make sure this is set to auto (your installer may have set this to a fixed output because your heat loss is approx 10kW and your current flow rate coincides with 10kW at delta T 5). In auto the Config CH Build Pump will target the max/nominal flow rate, but if it had been adjusted, it won't.

 

Then let us know.

[jamesdiyer]

 

19 minutes ago, SimonD said:

 

 

 

Then let us know.

 

Thank you very much for this advice. 

 

When the installer was here, we set pump to 100% and it flowed 1700l/h around heating circuit. 2000l/h around DHW circuit. 

 

Currently I'm Curve 0.6, desired temp 20C, room temp inactive, low flow 25, max flow 50. While I try to get it adjusted. We are a South facing rectangle so I will need to move to active to accommodate for sunny days.

 

No TRVs. Fully open. 1 circuit, branches into two 22mm mains feeding 5 radiators each - upstairs and downstairs.

 

I know I can meet my current heat loss, but I speced a 15kw machine as in a year or two I'll finish renovating the third floor - 100m2 independent apartment and this will need heating.  

 

I note your points on getting it working full bore and will try tomorrow. But I'm not sure I can get a kW reading from the software of vaillant screen? Though I guess I can read flow temps and flow rate and calculate. 

Edited 8 hours ago by jamesdiyer

[jamesdiyer]

Yes it's set to auto for pump. 

 

Is the fan rate an indication of if the machine is at 100%? Or perhaps it's compressions modulation %

 

I'm doing DHW cycle now and pump is 100%, compressor 70% and flow is 1640l/h / Ft 50.9C / Rt 43.4C ; so 14.26kW at delta 7.5C.

 

It is 19C outside. 

Edited 7 hours ago by jamesdiyer

[JamesPa]

10 minutes ago, jamesdiyer said:

Is the fan rate an indication of if the machine is at 100%? 

Live monitor-compressor modulation on the hoai is what you want.  The left hand bar on the hpai display when it's not displaying a menu also gives a visual indication.

 

If you want it to go full whack for any length of time you will need provide a load! Open your windows, turn off room influence, remove trv heads, turn any thermostats to max, operate at fixed ft equal to or above the ft at your design oat.  House should heat up to 30C or so.  Alternatively you may be able to force 100% compressor modulation in the installer test menu.

Edited 7 hours ago by JamesPa

[jamesdiyer]

This is a fantastic video by John cantor on dt and flow. And really confirms that I want more flow, to me anyway. 

 

I think we will be ok with the current flow we have, but when I want a greater heat demand I will need more flow, and having the ability to flow more - with a modulating pump speed - is never a bad thing. But maybe I've miss understood. Like having a car with a big engine, you might only want it occasionally to overtake, but when you need it you need it. 

 

 

 

I thinl

[jamesdiyer]

On 16/10/2025 at 11:32, sharpener said:

 

Not sure where you are as you post the pump performance in Spanish! In the UK the largest Arotherm plus is 12kW which is what I have. The primaries are in 28mm (o/d) and are about 10 m to the point where the circuits split into 22mm to the rads and 22mm to the UFH. The pump in the outdoor unit is very powerful, we see flow rates >2000 l/hr and it all works fine, I don't think you have fundamental cause to worry with what they are doing. If they have economised by using a cheap filter get it changed to a decent Magflow, Inta or Adey one and keep it clean.

Here is a flow/pressure calculator which may be handy.

 

The other useful relationship is 1 kWh = 860 litre-degrees i.e. 1kW = 860 degree-litres/h.

 

To pick up the filter situation. I have a standard strainer filter before the ashp. Would it be ok to remove this filter for a short period to test flow rate difference? Or do I run risk? 

 

 

Edited 2 hours ago by jamesdiyer

[JohnMo]

17 minutes ago, jamesdiyer said:

remove this filter for a short period to test flow rate difference? Or do I run risk? 

I would take it out, look at how dirty it is, give it a good clean, put back in a rerun, for an hour (check before and after flow rate), then check again, if clean, remove and do a quick run to look at flow rate.

 

All those pipes need external (UV resistant) insulation.

[jamesdiyer]

Just now, JohnMo said:

I would take it out, look at how dirty it is, give it a good clean, put back in a rerun, for an hour (check before and after flow rate), then check again, if clean, remove and do a quick run to look at flow rate.

 

All those pipes need external (UV resistant) insulation.

Thanks for suggestion will try. 

 

And yes the pipes are on the snagging list (they ran out of insulation). The rubber feet are also incorrect.