What is the overrun cutoff temperature for Gloworm Ultimate 50FF (+other questions and stats!)

[davegl]

Some background before my questions

I've a non condensing heat only Gloworm Ultimate 50FF boiler (22 years old) that feeds 2 x zone valves (CH & HW) and has a honeywell DM145 bypass valve. The pipe run from the boiler to the bypass valve/pump is 22mm and approx 16m total length (2 x 8m). For many years we have had the occasional boiler overheat cutout operate, and the gas engineer has swapped the cutout out at least twice and the main stat/pump overrun unit once, but then recommended setting the boiler stat to less than max, which historically for the most part has prevented tripping.

I've recently replaced a very noisy wilo pump with a new Grundfos Alpha3 and at the same time I fitted a new DM145 bypass valve (mainly because I had one and the position of the pump meant that the valve needed be undone to make access to the old pump easier). The Grundfos is really quiet, but you can see its working as it displays the mode and flow in m3/h. The advice from Grundfos was to leave the pump on 'auto adapt' which I did, but I've had problems with the overheat tripping when neither CH or HW is demanded and after the boiler had been firing for some time (i.e the circulating water was v hot at the time the last zone closed so it just relied on the bypass valve). From looking at the pump display I could see that on just bypass the flow read 0 m3/h (i.e no flow). At the weekend I changed to pump mode to operate at speed 2, and with just the bypass in circuit (set to the lowest value 1) it flowed at 0.7m3/hr (typically with all the rads open and CH demand the flow is 1.0m3/h). However the pump overun operated for just under 2 hours.

I recently bought a cheap digital temp meter and added two pipe clamp K probes to help me confirm my thoughts. I've checked the probes at 50degree C against a thermopen I have and they read true +/- 1degree so good enough for what I needed to do.

Findings and questions...

I fitted the clamps in the airing cupboard on the boiler flow and return pips (so approx 8m run to/from the boiler). With CH demanded, the flow temp steadily rose to 74-75 degrees then switched off, reduced to approx 67 then fired again (this was with the boiler stat set to MAX which the manual says is 82 degrees). The T1-T2 temperature was in the range 10-12 degrees so in spec (manual says aim for 11) and all rads were uniformly heated.

With the pump set to 'auto adapt' I removed all heating demand when the flow temperature (T1) read 60 degrees (i.e.before the boiler had cut off and cycled). The pump flow then read 0m3/h and a quick move of the clamps to either side of the bypass valve confirmed it hadn't opened (T1-T2 still approx 12 degrees). Moving the clamps back to the main feed (which in reality was not that far from being across the valve), I then saw the residual heat in the boiler cause T1 on the flow to rise in a couple of minutes by over 8 degrees. If I did the same test and removed the demand just as the boiler flow reached its maximum temperature (in my case about 75 degrees) the lack of any bypass flow caused the residual heat to get to 86 degrees at which point the overheat cutout tripped and once cooled needed to manually reset.

I then set the pump to speed two and repeated the tests. The bypass valve operated and the flow T1 measurement only went up 1 or 2 degrees then stabilised (so no trip). The pump showed a flow of about 0.7m3/h and within a few minutes the T1-T2 value was approx 1-2 degree (i.e very little heat loss in the bypass circuit).

I tracked the T1 temp and eventually when it dropped to 45 degrees the power to the pump was cut by the pump overrun. This took almost 2 hours, so a lot longer than the 'few minutes' manuals and other threads indicate, so....

Q1 - what is the typical temperature that the pump overrun circuit opens (in my current system each test has shown 44 / 45 degrees, and the time it runs for depends on the flow temperature when the bypass started). This means each time bypass is used, 2 hours of 15W energy is used in the pump

Q2. is my bypass circuit enough to cool the residual heat (basically 16m of 22mm pipe, the boiler, pump and bypass valve) - this was the design since new in 1994. How can I practically make it more efficient (this depends on the answer to Q1 because if the cutoff should be 60+ degrees then the time would be short enough).

Q3 - is the boiler stat max flow temp 75 degrees a realistic value or should it be higher - 80 degrees is suggested in the manual.

Q4 - what is the typical temperature for the overheat trip to operate (in my case it is currently 86 degrees which seems a bit close to 80 if any rise is expected when demand stops). The manual doesn't state a figure.

Q5 - what is the typical pressure value for the bypass valve - I've opted for the minimum as it only operates with no demand and I want the most flow (the CH has no TRV on the hall rad so that always provides a flow path when there is CH demand)

Q6 - should the grundfos Alpha3 operate a bypass valve when in 'auto adapt' - mine hasn't been, which is why we have had more trips since fitting it.

As an aside - I've also got the grundfos alpha reader that connects to the alpha3 and bluetooth's to a smart phone to balance the rads but I need to better determine some of my Rads BTU values. When I tried it over the weekend (before I had the pipe clamps) i had tried the app with a rad water temperature of 63degrees and it said the balanced flow wouldn't meet my target temperature ...so at the moment I've manually balanced to get the normal T1-T2 to be approx 11 degrees at flow and return. I'll try the process again once I settle on a max water temperature (currently 75 degrees not 63)

Thanks and sorry for so many words!

Dave

 

[davegl]

Well, I've just spend a 'fascinating' hour reading a thread from 2011 from'Smokebox' and gained some very useful info - including a statement that grundfos (in 20111 before the alpha3) said auto adapt was not compatable with automatic bypass valves (ABV as I now know to use) and that constant pressure mode (CP1 or 2) should be used. I've google searched for alpha3 and ABV and the only hits I get on the first page are to the alpha2L manual that confirms this (but that didn't have auto adapt mode). Also in the same 14 page thread MJN posted this useful link to a grundfos doc re ABVs that I also didn't find despite google searches and being registered on the grundfos training site.
http://www.newtonnet.co.uk/permanent/GrundfosDocs/SystemBypass.pdf

That 2011 thread was around a condensing boiler (mine isnt) but it seems to support what I found 0-flow temp is normally 75 degrees and that smart pumps autoadapt mode and ADVs are not compatible (despite an actual phone call I had with grundfos technical support before I bought the pump - i doubt I mentioned I had ABV because as far as I was aware all installations now needed them - the advice i was given ..with no caveats...- was to keep it on the default auto adapt mode).
Over the weekend I'll change it from fixed speed 2 to constant pressure 1 or 2 (i'll monitor the flow reading and temp delta)

The other thing I picked up from that old thread and the link was that that cast iron tanks hold a lot of heat and an ABV that routed the water to something useful (such as the HW system -27/1 EDIT - see later thread as for my layout this would not work) makes useful benefit of the pump overflow heat and (presumably) cools it quicker to stop the overrun. Given my pipe layout, I can easily change the pipework to do that (and from previously fitting my ABV the wrong way round I know it doesnt reverse flow!)

Dave

 

[PullerGas]

War & Peace!

Three words; Alpha are rubbish!!

The new Wilo ERP circulation pumps are more reliable than Grunny.

 

[AGAS]

anymore questions my dear chap ?

 

[davegl]

PullerGas -I know it was a 'bit' long but it helped me capture what I'd found and see the interaction (if any) with the tripping, new pump and new ABV .
I also had a thought overnight - if I were to route the ABV such that it used the HW circuit as I saw suggested in another old thread, in my case it would have a worse impact, as the boiler is heat only and I've a hot water cylinder which would then become a heat store and keep the bypass flow at 60 degrees until the whole 40+gallons cooled!. A better option (and also easy to do with some compresion fittings) for my layout would be to put the bypass in the rad side of the CH zone valve so that it can flow through at least the hall radiator.

I chose the Grundfos because of the experience with the older Wilo (and some negative reviews from users online and the grundfos +ve reviews on screwfix, but they recommended the alpha above the older UPS range). I didn't really find any good reviews for the WILOs - but presumably they were for older models as from confirmed buyers who had then replaced them. With the Alpha3 (I went for that after speaking to Grundfos tech support who did a good sales pitch on the benefits over the alpha2) it is working well and very quiet (now still in fixed speed 2 ), but time will tell re reliablity....but I agree tHat the technical benefit and associated higher cost of the auto adapt won't be relevant for me.

AGAS - no more questions but I will contact Gloworm to see if they have a stated pump overflow cut off temperature.

Dave

 

[PullerGas]

Without feeling compelled to read too much of your posts.

So, as someone that looks after several GW Ultimate boilers, another 3 words;
'Woods for trees'

You've a cast iron heat exchanger, a boiler thermostat set at Max & a variable head circulation (unreliable) pump. At the danger of missing something, while my eyes glazed over; is your system open vented?

 

[davegl]

yes its open vented with F&E tank in the attic . The system was installed in 1994 (new house)

 

[FlyingFish]

Off the top of my head, I'd be tempted to run the pump on a set speed like the system originally was setup. Your system is getting old so I'd be looking at possibly dropping the burner pressure. You could looking at the stat being slow to register temp increase before the limit stat kicks in, due to a furred up stat pocket. It's not prefect, but you need to be prepared to adjust as the system ages

 

[davegl]

Thanks for that flying fish-setting the stat to lower than max has been the previous solution to the trip out (which actually hasn't happened since I put the pump onto the set speed 2 rather than auto adapt earlier this week). Earlier today I changed the pump to constant pressure CP2 and will see what that does with regards stability and energy usage.

What I'm focussing on now is trying to determine if the overrun should run for so long as it does (not so much for energy but on a silent night you can hear the very quiet pump hum). The paper version of the boiler manual that came with the boiler and every Ultimate 50ff manual I can find online states the overrun is timed and the diagrams in the manual show a stat with 2 connections....but the actual diagram stuck to the slide out tray shows a 5 connector combined thermostat and overrun (which is what is fitted) - so I think I've got a mechanically driven overrun not PCB timed one.

 

[FlyingFish]

Sounds about right, get a service engineer to lower the BP. Then test with the stat on max and see if the stat clicks the burner off before the limit stat kicks in. This won't fix the pump overrun, but might lessen pesky resets of the boiler.