Grundfos Pump Occasionally Stalls on Willis based UFH system.

[TerryE]

Short version: We have an 8 year old passive-class all-electric house running on and optimised for the Octopus Agile tariff with electrically heated wet UFH. We made the house ASHP ready, but didn't install one during the build, instead using an inline Willis heater as a "temporary" solution to allow us to size the ASHP on actual house performance.  In practice the running costs are low enough that we've never made the RoI case to install an ASHP so here we are 8 years later and still using the Willis.  One of the major advantages of my design is that it has very few moving parts so pretty much no servicing maintenance is needed: some CU mounted contactors, some commercial ESP based modules, the Willis and the UFH pump. I keep cold-swap spares for the relays, modules and the Willis.  But now the pump has occasionally stalled.  Is it time to get a cold-swap spare or should I just have done and replace it?  @Nickfromwales   you are the oracle on such matters.

 

Longer supplementary.   My CH control system is a NodeRED based app comprising about 1K lines of JavaScript and some NodeRED flow including maybe 50-100 other NodeRED nodes -- a fairly small app by NodeRED standards. This uses MQTT to talk to the ESP modules and to share data with a Home Assistant instance which I use as a general Home automation interface. My basic strategy is to move any time-shiftable electricity loads to the cheapest Agile tariff time slots: white-goods, EV, HW and CH heating.   This is workable because the thermal capacity of the house is so high that it doesn't really matter when I schedule heating so long as I top up enough each day overall.  Each day just before tariff roll-over, the system calculates the heating required for the day ahead and allocates a heating schedule so that we do this at the cheapest price. So our typical electricity use is a base ripple of stuff that can't easily be time shifted, plus big blocks of power draw at the cheapest prices that day.  See the graph below which is an extract for 32 hours starting 4 AM yesterday.  The top plot is our spot energy use taken from our smart meter; the bottom plot is the Willis temp, plus the average out and return flow temps from the UFH loops. 

 

The cheapest price slot was 04:30 - 06:00 so that was when the main UFH heating slot was scheduled (the spike to 9kW spike was when the HW immersions also kicked in) )  You can see the typical UFH heating curve: The Willis quickly heats to ~27°C with the average out flow to the UFH a couple of degrees cooler and the return at 19°C (the overall slab temp); these all slowly rise together by about 2½°C over the next 90 mins as the heat transferred  warms the slab around the UFH pipe.  This pattern happens on four heating cycles during this period. 

 

BTW, the out & return flow temperature readings are steppy because these thermometers are only read if the circulation pump has been running for at least 5 mins, because  these rapidly settle to the ground-floor ambient temperatures without circulation.  The pump is  cycled for 6 mins every 3 hours to enable the slab temp to be tracked.

 

Note that some went wrong at 14:41  and the following 01:31. Here the Willis suddenly started heating rapidly until the 35 °C safety trip was exceeded and the CH system turned off the Willis.  The system log shows that the pump relay was still on but the water wasn't circulating: it had stalled at 14:41 and was still stalled when it came on again at 01:30.  What is odd is that it started correctly at the 3:30 heating slot, so the stall is intermittent .  Very odd.

 

 

Edited Wednesday at 11:59 by TerryE

[dpmiller]

what type of pump is it- fancy multimode thingy with digital display, or old tech with a 3-speed switch and a starting capacitor? Is the water well inhibited?

[TerryE]

It's a Grundfos UPM2 15-70 CIL2 that runs at about 40W.  Easy to bump start manually except that I am in Greece at the moment and my house is over 2,000 miles away in the UK, but back home in just over a week.  In the meantime, I've downloaded the manual for this model and will read it. I will also monitor the HA system to see if we get any more stalls.

 

The water is inhibited but there is little scope for electrolytic corrosion: no rads; just the PexAlPex going into the Wunda manifold and a short loop-back through the Willis.  The expansion vessel and fill input is T'd off this.

 

I need to give my live-in son some basic plumbing and home automation lessons.    🤣

Edited Wednesday at 20:36 by TerryE

[Nickfromwales]

The primary issue @TerryE is the short duty of the pump as running for only a couple/few months max means these stagnate and ‘stick’ quite annoyingly.

 

I had 3x UPM3’s do exactly this on a very high spec (£3.8m) PH+ project and I couldn’t work it out. Had to drive to West Sussex 3 times to get them all spinning again (manual strip down and spin with a pliers). Major unwanted cost to me, and a big piss me off!!

 

Eventually I realised these pumps do NOT like sitting still.

 

Solution there was a Shelley which was set to spin the pump for 60 seconds at 03:00 on the first day of each month. Had to use one per, to keep the switch lives apart.

 

No issues since.

 

Just so bloody much to think about with PH; pros / cons / caveats / gotcha’s etc.

 

#livingandlearning

 

[Nickfromwales]

@TerryE

 

You reminded me above you have HA. So will be simple for you to dial in some extra on / off prompts? You can dial in remotely from Greece lol. 😜 

[TerryE]

I do VPN into the house routinely to keep an eye on things. I've also got email alerting of any errors like this so I don't miss something on my TODO list.

 

I do cycle the pump for 6 mins every 3 hrs - mainly so that I can log the slab temp, but doing this routinely cycle the UFH and stops any crud selling out in the pipework or pump over the summer.

 

BTW, the Elec Installation sec of the pump manual warns that the pump can have an inrush spike of ~8A at on/off, so advises that any relay should be rated to handle this i.e. have AgSnO contacts (e.g. a contactor) so you might have cycle life issues with the Shelly causing it to fail after a few years. 

 

As to spinning these up, it's a two min job and there's even a YouTube howto on this. Next time send the customer a link and say this is a routine home owner job - or charger a hefty call out fee.

 

BTW if you are passing the MK area and need an overnight / nice meal then give me a shout - so long as we are in country that is. 😄

[Gus Potter]

On 01/10/2025 at 12:57, TerryE said:

One of the major advantages of my design is that it has very few moving parts

That is the secret of any UFH design. 

 

I'm still going to be a philistine and say you UFH needs to be workable for 60 years, cheep and easy to maintain. So we need short loops with long tails coming up from the floor.

 

 

In the grand scheme of things I think much of the stuff I see on BH about electronics is bollocks. Most of it will work for say 5 -7 years, any software will almost be impossible to update. What planet do you live on! I'll say again I was into this when some of you were not even born.. 50 - 60 year service life is the target to preserve tour asset value. The pipes can las tthat long.. con=mpare with steel radiators say 15 years. 

 

I've just taken on a new Client that has bought a house that is filled with home automation, it's out dated, yes it contains lots of at the time state of the art and very expensive shite.. and it's all going in the skip.

 

It astounds me that folk think that this home automation, apparently clever UF design is actually going to add value to your house.. to me, yes indulge your hobby, but no way is anyone going to pay extra for your automation and control stuff, rather they will write it down and often treat it as a liability. 

 

To design a UFH system that will last.. we need short loops, redundancy, put extra pipes at external doors where the cold comes in. You can stick your loop cad up your own pipe and start to trust your common sense. 

 

Honestly I look at some of these posts and think.. aye right!

 

But can anyone here tell me how and how often the performance of your fancy UFH system with weather compensation has changed and how often after five years they are having to replace the valves and update their software, put in loads of inhibitor .. you won't as you'll be too embaressed I guess. Now what about say 7 years.. any takers here. 

 

Honestly I think some folk on BH need to start thinking about maintenence cost before professing about their knowledge as folk on a budget may think that you are giving good investment advice when in fact your just indulging in your fantacy and basically gas lighting folk. 

 

So any takers to come up with long term maintainence costs to rip me to shreads? Go on give it a go and take a 7 year cycle..then look at ten years.. 

 

 

 

 

 

 

 

[Oz07]

Why short loops @Gus Potter?

[John Carroll]

On 01/10/2025 at 21:31, TerryE said:

It's a Grundfos UPM2 15-70 CIL2 that runs at about 40W.  Easy to bump start manually except that I am in Greece at the moment and my house is over 2,000 miles away in the UK, but back home in just over a week.  In the meantime, I've downloaded the manual for this model and will read it. I will also monitor the HA system to see if we get any more stalls.

 

The water is inhibited but there is little scope for electrolytic corrosion: no rads; just the PexAlPex going into the Wunda manifold and a short loop-back through the Willis.  The expansion vessel and fill input is T'd off this.

 

I need to give my live-in son some basic plumbing and home automation lessons.    🤣

 

The Grundfos UPM seems a very popular choice of circulator for UFH, wonder why since one would think that any pump with constant pressure mode/settings would do the job.

Can you remotely see if the system pressure is normal?. Assume the Willis is installed correctly, with the immersion head on the bottom with the inlet on the side and the outlet straight out the top, otherwise air can build up if installed incorrectly, may not be a huge problem with the sealed pumped system.

[TerryE]

@Gus Potter, I agree with you in many respects, but also take an opposite view on some.  I had just turned 65 when we moved in.  Doing a self-build was only feasible for us at this stage in life when we had enough capital and time and effort available to take of some of the trades and jobs ourselves to reduce cost.

 

You mention a 50-60 year objective, but we optimised for about 30 years, as I doubt we'll be around much longer than that.  We put a lot of thought into our design and material choices to ensure that the house would be pretty much zero maintenance for that sort of time-frame, but the house should be good for at least another 30-50.

 

If you are talking about a 50 year horizon, then the other key point is that the house has to be electric only -- which it is.  The number of UFH loops is just a small design detail that should be matched to the house characteristics. In our case we need to put about 2kW (coldest midwinter) into the slab to keep the entire house at a cosy 22+°C, so 3×95m loops controlled as a single zone works fine for us.  The UFH tail length (if long enough) is pretty irrelevant.  I feel that your position about automation is about similar to the argument that our predecessors might have had 100 years ago about replacing gas and paraffin heating and lighting by electricity.  Technology moves on, so reject it and get stuck in the past or accept and embrace it: this is a personal choice.  In my case, our design choices reflect some principles (like all-electric and near zero maintenance), but beyond this they were largely driven by return on investment (RoI) criteria: I have minimised our running costs, and we won't invest in "improvements" unless the discounted savings over a 10-year per period exceed the net investment cost.

 

BTW, I wrote my first computer program 57 years ago and my career was spent in IT so I am very familiar with programming and approaches such as integrated logistic life cycle management.  This is why, for example, my CH system is independent of my Home Assistant (HA) stuff; why at a component/module level everything is pretty-standard multi-source commercial off-the-shelf, and i keep enough spares to be able to do cold-swap repair in less that 24 hrs.

 

Putative new buyers could rip out all of the HA system and its IoT devices, but this would leave them a working CH and HW system. They could replace the entire CH / HW control system for under £2K if they stuck with resistive heating, or by then Octopus will probably have a bundled deal to install an ASHP with demand-side managing your CH, HW and EV on some flat-rate tariff.

[Temp]

Do these 

On 01/10/2025 at 18:58, dpmiller said:

what type of pump is it- fancy multimode thingy with digital display, or old tech with a 3-speed switch and a starting capacitor? Is the water well inhibited?

 

+1 

 

I'd have it out to see if there is lots of scale, perhaps descale it. Perhaps replace the starter capacitor. If that doesn't work replace the pump.

 

 

[dpmiller]

^ electronically commutated, no capacitor. Doesn't look like it's got any unblocking mode unlike many modern pumps that'll attempt to shake themselves loose if the rotor can't move?

[TerryE]

9 hours ago, John Carroll said:

Can you remotely see if the system pressure is normal?.

John, I pressured the UVH to 1 bar on commissioning and topped after initial dissolved air bleed off.   I haven't needed  to top up since.  I chose 1-bar because the Pump spec called for a min ½ bar and I could see any advantage in going above 1.  The circulation is on the lowest pump setting and this seems to circulate the water fast enough.  A good safely check is the willis temp as this rapidly climbs if the pump isn't circulating the water through the slab, and I do have a safety check on this.

[John Carroll]

Something not adding up there Terry assuming you have a A rated pump.

You say you have 3 x 95M loops, assuming 16mm pipe, 12mmID, and assuming a flowrate of 2.5LPM/loop then the friction loss is ~ 1.7M/loop, add 15% for bends etc gives ~ 2.0M loss, 3 loops X 2.5LPM = 7.5LPM, 0.45m3/hr, so the pump must deliver 0.45m3/hr at a 2M head. If your pump curves look like the ones below then the power required should only be around 12W yet your pump is pulling ~ 40W, pump may be on the way out or else, for some reason or other its running with over a 6M head to draw 40W at ~ 0.45m3/hr.

 

[Nickfromwales]

18 hours ago, TerryE said:

I do VPN into the house routinely to keep an eye on things. I've also got email alerting of any errors like this so I don't miss something on my TODO list.

 

I do cycle the pump for 6 mins every 3 hrs - mainly so that I can log the slab temp, but doing this routinely cycle the UFH and stops any crud selling out in the pipework or pump over the summer.

 

BTW, the Elec Installation sec of the pump manual warns that the pump can have an inrush spike of ~8A at on/off, so advises that any relay should be rated to handle this i.e. have AgSnO contacts (e.g. a contactor) so you might have cycle life issues with the Shelly causing it to fail after a few years. 

 

As to spinning these up, it's a two min job and there's even a YouTube howto on this. Next time send the customer a link and say this is a routine home owner job - or charger a hefty call out fee.

 

BTW if you are passing the MK area and need an overnight / nice meal then give me a shout - so long as we are in country that is. 😄

Got one on the go (certified PH) in Bow Brickhill, but that’s on stop atm as they ran out of funds.

 

I’ll seek you out when they find the pot of gold they need to get going again….not holding my breath atm though  

[TerryE]

5 hours ago, John Carroll said:

If your pump curves look like the ones below then the power required should only be around 12W yet your pump is pulling ~ 40W,

Thanks for this, but I made a cock-up and hang my head in shame. I am getting a bit old after all. 🫣😨 

 

I pulled the wrong pump photo from my house pictures.  That was a pic of the pump in my old SunAmps which as you say is PCM controlled.  My house is 2,000 miles away and I pulled the wrong pic.  It's working fine at the mo, so this can wait until I get back on the 12th.  I will update then.

 

Sorry guys. 

 

PS I think it is a UPS2 25/40-60 130.  This has an 240VAC input and H/M/L selector for speed control.  😨

Edited Friday at 22:44 by TerryE

[John Carroll]

 

The UPS2 should require ~ 23W at the above flowrates on minimum fixed speed, 4M head.

 

 

[TerryE]

@John Carroll thanks 

[Gus Potter]

Hi Terry.

 

First, thanks from me for the effort you have put in to make your post. It takes time to write this way so appreciate the time it takes.

 

This is Buildhub and if we were all to agree then it would die off pretty quick. I often argue for simplicity, make the case for simple stupid and yes that comes at a slightly reduced performance initially but after 5 - 10 years then I do think I'm in strong position to make a valid case. I designed my own self build UFH 30 years ago so I'm not inexperienced. I'm also and SE / past conctractor so can, if pushed can draw on hard commercial facts about buildability and how you often want to keep your market options open as a self builder. 

 

For all on BH, always keep an eye on not just cost but the buidability and long term performance.  Self building is about saving money and compromising. There are some on BH that are worth millions, but they still monitor cost and buildability. 

 

On 03/10/2025 at 13:18, TerryE said:

I agree with you in many respects, but also take an opposite view on some.  I had just turned 65 when we moved in.  Doing a self-build was only feasible for us at this stage in life when we had enough capital and time and effort available to take of some of the trades and jobs ourselves to reduce cost.

 

You mention a 50-60 year objective, but we optimised for about 30 years, as I doubt we'll be around much longer than that.  We put a lot of thought into our design and material choices to ensure that the house would be pretty much zero maintenance for that sort of time-frame, but the house should be good for at least another 30-50.

 

If you are talking about a 50 year horizon, then the other key point is that the house has to be electric only -- which it is.  The number of UFH loops is just a small design detail that should be matched to the house characteristics. In our case we need to put about 2kW (coldest midwinter) into the slab to keep the entire house at a cosy 22+°C, so 3×95m loops controlled as a single zone works fine for us.  The UFH tail length (if long enough) is pretty irrelevant.  I feel that your position about automation is about similar to the argument that our predecessors might have had 100 years ago about replacing gas and paraffin heating and lighting by electricity.  Technology moves on, so reject it and get stuck in the past or accept and embrace it: this is a personal choice.  In my case, our design choices reflect some principles (like all-electric and near zero maintenance), but beyond this they were largely driven by return on investment (RoI) criteria: I have minimised our running costs, and we won't invest in "improvements" unless the discounted savings over a 10-year per period exceed the net investment cost.

 

BTW, I wrote my first computer program 57 years ago and my career was spent in IT so I am very familiar with programming and approaches such as integrated logistic life cycle management.  This is why, for example, my CH system is independent of my Home Assistant (HA) stuff; why at a component/module level everything is pretty-standard multi-source commercial off-the-shelf, and i keep enough spares to be able to do cold-swap repair in less that 24 hrs.

 

Putative new buyers could rip out all of the HA system and its IoT devices, but this would leave them a working CH and HW system. They could replace the entire CH / HW control system for under £2K if they stuck with resistive heating, or by then Octopus will probably have a bundled deal to install an ASHP with demand-side managing your CH, HW and EV on some flat-rate tariff

@TerryE"I had just turned 65 when we moved in.  Doing a self-build was only feasible for us at this stage in life when we had enough capital and time and effort available to take of some of the trades and jobs ourselves to reduce cost."

 

Fab, love this! I think you'll be well rewarded. Some folk self build to make money, some do it to build the dream.. sometimes it takes a working life to indentify what that dream house is!

 

"If you are talking about a 50 year horizon,." My primary qualification is a Civil Enginner.. I work for the general good so take a different view at times. 

 

@TerryE  I feel that your position about automation is about similar to the argument that our predecessors might have had 100 years ago about replacing gas and paraffin heating and lighting by electricity.  Technology moves on, so reject it and get stuck in the past or accept and embrace it: this is a personal choice.  In my case, our design choices reflect some principles (like all-electric and near zero maintenance), but beyond this they were largely driven by return on investment (RoI) criteria: I have minimised our running costs, and we won't invest in "improvements" unless the discounted savings over a 10-year per period exceed the net investment cost.

 

@TerryEYou can reject my argument all you want, in this case you, I think,  are making the straw man argument and I'm not falling for it. You're all electric apporach sounds idiot proof. But if you look back on my previous posts you'll see I've never critised all electic UF. But.. it's your house and your money. 

 

I'm not giving in here folks. Can anyone tell me if they have any idea what the ongoing maintenance cost of automated UF is over 10 years when the moving parts and software gets out dated. Remember that these UF pipes are buiried in the structure and need to last a LONG time.. come on anyone? 

 

So my design ethos for wet UF is, put in plenty shortish  loops, the pipes are not that expensive, build in redundancy.. we are only talking about a few hundred extra in pipe cost. Do that and your UF will be a joy, take care of it's self. Think ahead.. 

 

@TerryE  feel that your position about automation is about similar to the argument that our predecessors might have had 100 years ago about replacing gas

 

No I'm not stuck in the past.. but my past experience of UF, when most folk, on BH had never heard of it, education allows me to think how will I deal with the future.. if you can't see that then more fool you.

 

Often my arguement is about trying to get folk to think pragmatically, but also innovatively, often good design is to build the things in with the bricks that you can change and in the case of UFH give plenty length of tales, redundancy so as the energy market changes it allows you to swap the method of energy delivery easily in say 20 years time. 

 

I honestly despair at the folk that are calculating the UFH output to the nearest watt.. it's all bollocks in real life! And for that I'll take the flack.. but it's not my money folks.. it's YOURS!