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High Limit Stat tripping

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    #32
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    Blowheads wrote: »
    Would check having a AAV on the boiler, newer ones have them inbuilt.

    You would need to know the return flow temperature to know the water is not dissipating the heat

    Is there a bypass fitted? Just a loop on itself to allow the pump to circulate water if all valves closed

    Is there a frost stat? What that set at?

    For the boiler dual stat, few things to try, turn down number to 1.5 maybe, ( mine runs from 55 to 90) so 2.5 should be ~75. I turned mine back down to 65.
    Maybe also consider to replace the dual stat, they can deteriorate
    Check the hole for the stat is not dirty

    No AAV fitted, it is warmflow whitebird utility model so no frost stat either. Will turn down dual stat and see how we go.


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    #33
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    John.G wrote: »
    Yes you actually did say in your post No11 that its HM Pro 4-7 set @ PP6, I would change it to fixed pressure FP and try it at different settings starting as you suggest at a low setting and gradually increasing it but even if there is a restriction the pump should't have modulated below 2 to 3 M at minimum on PP6 which should still be quite OK to to give adequate circulation through the cylinder coil.
    You also stated in post1 that the water in and out of the coil is warm, unless there is a total/huge restriction somewhere then the water in (whatever about out) to the coil should be be roasting hot....as hot as it leaves the boiler or pump almost, if its only warm where it enters the cylinder then there is only a trickle getting through and its no wonder the hi limit stat is operating.
    http://www.heatmerchants.ie/v4/581ae913-e1fb-435e-a88b-ded312da5b38/uploads/HM%20PROflyer.pdf

    Will change settings as suggested and pick up a temp guage and see how the temperature are running.


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    #34
    jimf
    Registered Users Posts: 3,950 ✭✭✭jimf


    THE ALM wrote: »
    No AAV fitted, it is warmflow whitebird utility model so no frost stat either. Will turn down dual stat and see how we go.

    warmflow stats are known to have intermittent problems as they age


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    #35
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    THE ALM wrote: »
    Will change settings as suggested and pick up a temp guage and see how the temperature are running.

    Carried out test on my own cylinder there now, 150 Litre cylinder fitted with 0.65 M2 coil, I shut off all the rad circuits and opened the coil motorized valve manually and let the cylinder heat up to whatever it could as I was trying to simulate a limescale covered coil with little or no heat transfer, Oil boiler cutin/cutout was 75C/63C cylinder water temperature was 63C, flow/return pipes to coil were both fluctuating with the boiler temperature and both were fluctuating between 71C and 59C, I couldn't measure any difference between the flow and return measured with a infa red scanner. I left the system like that for over a hour and the boiler cycled twice in that period and did not operate the hi limit stat (set to 110C/115C).
    This just MIGHT indicate that as long as there is circulation through the boiler even with little or no heat transfer then it will not come out on the hi limit stat, in other words the coil was acting like a by pass.
    But as jimf states with faulty/unreliable boiler stats even though not operating with rads in circuit and is operating on cylinder only perhaps due to the higher
    soak temperature?. Or else there is a big restriction somewhere, who knows?.


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    #36
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    John.G wrote: »
    Carried out test on my own cylinder there now, 150 Litre cylinder fitted with 0.65 M2 coil, I shut off all the rad circuits and opened the coil motorized valve manually and let the cylinder heat up to whatever it could as I was trying to simulate a limescale covered coil with little or no heat transfer, Oil boiler cutin/cutout was 75C/63C cylinder water temperature was 63C, flow/return pipes to coil were both fluctuating with the boiler temperature and both were fluctuating between 71C and 59C, I couldn't measure any difference between the flow and return measured with a infa red scanner. I left the system like that for over a hour and the boiler cycled twice in that period and did not operate the hi limit stat (set to 110C/115C).
    This just MIGHT indicate that as long as there is circulation through the boiler even with little or no heat transfer then it will not come out on the hi limit stat, in other words the coil was acting like a by pass.
    But as jimf states with faulty/unreliable boiler stats even though not operating with rads in circuit and is operating on cylinder only perhaps due to the higher
    soak temperature?. Or else there is a big restriction somewhere, who knows?.

    Thanks John.G for the testing. Need to pick up a thermometer and do a bit more detailed testing and try to narrow it down.


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    #37
    Wearb
    Moderators, Home & Garden Moderators Posts: 6,213 Mod ✭✭✭✭Wearb


    John.G wrote: »
    Carried out test on my own cylinder there now, 150 Litre cylinder fitted with 0.65 M2 coil, I shut off all the rad circuits and opened the coil motorized valve manually and let the cylinder heat up to whatever it could as I was trying to simulate a limescale covered coil with little or no heat transfer, Oil boiler cutin/cutout was 75C/63C cylinder water temperature was 63C, flow/return pipes to coil were both fluctuating with the boiler temperature and both were fluctuating between 71C and 59C, I couldn't measure any difference between the flow and return measured with a infa red scanner. I left the system like that for over a hour and the boiler cycled twice in that period and did not operate the hi limit stat (set to 110C/115C).
    This just MIGHT indicate that as long as there is circulation through the boiler even with little or no heat transfer then it will not come out on the hi limit stat, in other words the coil was acting like a by pass.
    But as jimf states with faulty/unreliable boiler stats even though not operating with rads in circuit and is operating on cylinder only perhaps due to the higher
    soak temperature?. Or else there is a big restriction somewhere, who knows?.
    Are you saying that you couldn't measure it with the scanner, but could with something else?

    Please follow site and charter rules. "Resistance is futile"



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    #38
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    Wearb wrote: »
    Are you saying that you couldn't measure it with the scanner, but could with something else?

    No, I just couldn,t detect any measurable difference between the COIL flow & return temperatures using my contact type infra red microscanner.


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    #39
    whizbang
    Registered Users Posts: 1,924 ✭✭✭whizbang


    I put some temp sensors on my flow and return piping, beside the cylinder coil, and logged over a few days.

    What's immediately obvious, is there is less difference in the temperatures when probes are nearer to the coil. When the burner is firing and pump running, its easier to see the differences. The further away from the coil, the bigger the differences.

    Interestingly when the immersion heater was on(outside temp too high for heating) both pipes showed the increase, even though the motorised valve for coil was off.

    It appears to me the copper is conducting the heat better than the water.


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    #40
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    whizbang wrote: »
    I put some temp sensors on my flow and return piping, beside the cylinder coil, and logged over a few days.

    What's immediately obvious, is there is less difference in the temperatures when probes are nearer to the coil. When the burner is firing and pump running, its easier to see the differences. The further away from the coil, the bigger the differences.

    Interestingly when the immersion heater was on(outside temp too high for heating) both pipes showed the increase, even though the motorised valve for coil was off.

    It appears to me the copper is conducting the heat better than the water.

    What kind of coil temp differences (DeltaT) were you getting obviously with the boiler in service??.

    I came across a very detailed record of tests that I carried out in 2015, these readings would have been very accurate apart from the Coil flow rate which I can't measure but it certainly wouldn't have been more than 10 LPM with rads+cylinder coil circuits in use together.
    Its interesting in that the coil power was > 7 Kw with a cold cylinder at 13C and only 2.4 Kw with a "hot" cylinder at 56C. due to the decreasing deltaT between the coil and the cylinder water. In all cases though there is certainly a
    very measurable coil deltaT if one has the correct probes and that,s why I am interested in your numbers.


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    #41
    whizbang
    Registered Users Posts: 1,924 ✭✭✭whizbang


    RadTemps.jpg
    Sorry its not what you are looking for. Just the Radiator circuit Flow and return, logged over a few days.
    I didnt bother logging the temps at the cylinder, there was too little differences visible.
    I suspect the return may not be as low as shown, the handiest place for sensor was on the bottom of the shutoff valve body.
    Pump is UPS2 proportional sensing mode.

    I cant get excel to correctly display date/time so ignore...


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    #42
    whizbang
    Registered Users Posts: 1,924 ✭✭✭whizbang


    RadTemps19.jpg
    Heres a closeup of 19/10/18

    How do i display these pics??


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    #43
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    whizbang wrote: »
    RadTemps19.jpg
    Heres a closeup of 19/10/18

    How do i display these pics??

    Pics look fine to me as is, the flow temp reflects the boiler stat hysteresis? with the return fairly steady due to the rad(s) acting like a thermal store?. It would be very interesting to see the cylinder coil readings with the probes attached ~ 6 ins away from the cylinder especially with pump on PP control and the cylinder zone only on.


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    #44
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    Got the use of a infrared thermometer yesterday evening so hopefully be able to take a few readings this evening.

    I did turn the settings on the pump to fixed pressure at setting 2 as suggested and found the the boiler would knock itself off after 5-6mins and the flow from boiler was extremely hot at this point so will take a few readings and see what the temp is at various points on the system.


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    #45
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    THE ALM wrote: »
    Got the use of a infrared thermometer yesterday evening so hopefully be able to take a few readings this evening.

    I did turn the settings on the pump to fixed pressure at setting 2 as suggested and found the the boiler would knock itself off after 5-6mins and the flow from boiler was extremely hot at this point so will take a few readings and see what the temp is at various points on the system.

    Was the boiler cutting out or tripping out on the Hi limit stat?.


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    #46
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    John.G wrote: »
    Was the boiler cutting out or tripping out on the Hi limit stat?.

    cutting out John.G


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    #47
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    THE ALM wrote: »
    cutting out John.G

    At least I think one can conclude from that; that there is some circulation through the coil, a 5/6 minute oil boiler run with cylinder zone on only isn't unduly short IMO. Even with a clean/unrestricted flow as the boiler, depending on size, will be outputting 20 to 30 Kw and the coil depending on the hot water cylinder temperature will only absorb ~ 1.5/8 Kw.
    It will be very interesting to see what the scanner shows up.


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    #48
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    John.G wrote: »
    At least I think one can conclude from that; that there is some circulation through the coil, a 5/6 minute oil boiler run with cylinder zone on only isn't unduly short IMO. Even with a clean/unrestricted flow as the boiler, depending on size, will be outputting 20 to 30 Kw and the coil depending on the hot water cylinder temperature will only absorb ~ 1.5/8 Kw.
    It will be very interesting to see what the scanner shows up.

    Thanks John.G, will be interesting to see alright. Will also measure temp of cyclinder to see what sort of temp the water is reaching.


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    #49
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    temp_readings.jpegManaged to get a couple of readings last night.

    At this stage the ch & hw had been running together for about 30mins and this is about another 10mins later when the hw pump had been running on its own. I have taken the readings at the isolator valve bodies above and below the pump and at the fittings to and from the cylinder and at the brass coupling on the return.

    I notice when taking these that before the boiler would have tripped out whereas now it did go off and fire up again in the time, 20mins approx, that I was taking the various readings.


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    #50
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    THE ALM wrote: »
    temp_readings.jpegManaged to get a couple of readings last night.

    At this stage the ch & hw had been running together for about 30mins and this is about another 10mins later when the hw pump had been running on its own. I have taken the readings at the isolator valve bodies above and below the pump and at the fittings to and from the cylinder and at the brass coupling on the return.

    I notice when taking these that before the boiler would have tripped out whereas now it did go off and fire up again in the time, 20mins approx, that I was taking the various readings.

    My reading of this is: 63.7C & 63.3C are the temps at the circ pump, the 57.2C is the return temp from the cylinder coil, the 51.4C & 56.2C are the cylinder coil Flow & return temps?. What does the 42.1c & 41.9C refer to?.
    Also IF the 51.4C & the 56.2C refer to the coil temps then it would seem that the coil flow is from bottom to top.

    Edit: The 42.1C & 41.9C are probably referring to the CH Pump??


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    #51
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    John.G wrote: »
    My reading of this is: 63.7C & 63.3C are the temps at the circ pump, the 57.2C is the return temp from the cylinder coil, the 51.4C & 56.2C are the cylinder coil Flow & return temps?. What does the 42.1c & 41.9C refer to?.
    Also IF the 51.4C & the 56.2C refer to the coil temps then it would seem that the coil flow is from bottom to top.

    Edit: The 42.1C & 41.9C are probably referring to the CH Pump??

    Correct John.G, CH pump is the other reading after that pump had stopped running, just showing as a comparison. Looks like the flow in the coil is from bottom to top and I took a few readings and top was always cooler than bottom.


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    #52
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    THE ALM wrote: »
    Correct John.G, CH pump is the other reading after that pump had stopped running, just showing as a comparison. Looks like the flow in the coil is from bottom to top and I took a few readings and top was always cooler than bottom.

    Did you take any reading(s) from the cylinder itself?, it would be interesting to see it.
    The average of the pump temps (63.5C) minus the return of 57.2C gives a coil deltaT of 6.3C and the deltaT at the coil (56.2-51.4), 4.8C so not hugely different so average the two at 5.6C, I would expect that circ pump if not restricted at speed 2 to give a flow rate of at least 10 LPM, this would give a coil power of 3.9 KW which IF the cylinder is/was at ~ 45/50C is good heat transfer. Of course if the flow rate is very low for whatever reason then the above doesn't apply.
    As your cylinder never gets very hot and takes hours to heat up then it possibly points to a flow rate problem (NR valve?).
    The reversed flow through the coil (bottom to top) while unconventional shouldn't IMO be the cause of the problem as its a pumped flow.

    You could also monitor the cylinder temperature rise/rate and calculate the heat its absorbing once you know its volume.


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    #53
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    Thanks again John.G for your input. I feel I am heading towards a drain down and check of the NRV:eek:

    Not the end of the world and at least the exercise as been useful and limited where the problem could be. Temperature look ok and probably about what I would expect.


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    #54
    whizbang
    Registered Users Posts: 1,924 ✭✭✭whizbang


    Sorry OP, gone derailed..

    JohnG;
    Graphs of cylinder supply and return pipework.
    Both sensors placed about 4" from Cylinder. Flow sensor is on the T to rads and cylinder, Return is upstream of zone valve.
    Valve controller is just timer thermostat, no call for heat, with Rads always on(some on thermostatic)
    Cylinder thermo sensor is about 3" below the top, just where the wall starts to curve in.
    Start of day, temp approx 36degC, end of day about 44degC.


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    #55
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    whizbang wrote: »
    Sorry OP, gone derailed..

    JohnG;
    Graphs of cylinder supply and return pipework.
    Both sensors placed about 4" from Cylinder. Flow sensor is on the T to rads and cylinder, Return is upstream of zone valve.
    Valve controller is just timer thermostat, no call for heat, with Rads always on(some on thermostatic)
    Cylinder thermo sensor is about 3" below the top, just where the wall starts to curve in.
    Start of day, temp approx 36degC, end of day about 44degC.

    Thanks for that, it might appear that your "average" coil deltaT at around 0936 (first trend) is around 5.5C??.

    The OP is attempting to see if his slow heat up time is caused by a limescaled coil or if there is some restriction in the flow rate to the coil, as you will see by his posts he is removing/inspecting the NR valve after the circ pump to see if that is the problem, his coil deltaT is averaging around 5.6C.
    As I said if one assumes a minimum flowrate of 10 LPM then the coil should be absorbing 3.9 Kw which should give a reasonable heat up time, if the coil is only absorbing say ~ 1 Kw (very slow heating time) then either the flowrate is
    very much restricted or the coil is lime covered but if so then for that same flowrate of 10 LPM and 1 Kw, the coil deltaT could only be ~ 1.5C.
    That's the conundrum.


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    #56
    hatchman
    Registered Users Posts: 317 ✭✭hatchman


    John.G wrote:
    The OP is attempting to see if his slow heat up time is caused by a limescaled coil or if there is some restriction in the flow rate to the coil, as you will see by his posts he is removing/inspecting the NR valve after the circ pump to see if that is the problem, his coil deltaT is averaging around 5.6C. As I said if one assumes a minimum flowrate of 10 LPM then the coil should be absorbing 3.9 Kw which should give a reasonable heat up time, if the coil is only absorbing say ~ 1 Kw (very slow heating time) then either the flowrate is very much restricted or the coil is lime covered but if so then for that same flowrate of 10 LPM and 1 Kw, the coil deltaT could only be ~ 1.5C. That's the conundrum.


    Can op drain down cylinder and inspect coil by removing immersion? I had similar situation with my cylinder on geothermal heat pump. I opened inspection panel on cylinder sure I was going to find limescale on coil. But coil was clean post refill issue disappeared.


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    #57
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    hatchman wrote: »
    Can op drain down cylinder and inspect coil by removing immersion? I had similar situation with my cylinder on geothermal heat pump. I opened inspection panel on cylinder sure I was going to find limescale on coil. But coil was clean post refill issue disappeared.

    hatchman, that is another avenue I am contemplating and wondering would removing the immersion or NRV be easier.

    I am getting hot water by running the heating and hot water in conjunction, just not as efficiently as I would expect and running the hw on its own can sometimes trip the boiler.

    As we are heading into a colder time of the year, rather than playing around with it, I may leave it for now and revisit in the spring as we wouldn't want to be without heating for any length on time.


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    #58
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    THE ALM wrote: »
    hatchman, that is another avenue I am contemplating and wondering would removing the immersion or NRV be easier.

    I am getting hot water by running the heating and hot water in conjunction, just not as efficiently as I would expect and running the hw on its own can sometimes trip the boiler.

    As we are heading into a colder time of the year, rather than playing around with it, I may leave it for now and revisit in the spring as we wouldn't want to be without heating for any length on time.

    Removing the immersion in theory is quite easy but can be fraught with problems ie danger of distorting/twisting the cylinder top itself, if considering doing it, just run off the hot water but let the cylinder "full" until you slacken off the immersion with a "spanner" that you can apply a couple to.


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    #59
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    John.G wrote: »
    Removing the immersion in theory is quite easy but can be fraught with problems ie danger of distorting/twisting the cylinder top itself, if considering doing it, just run off the hot water but let the cylinder "full" until you slacken off the immersion with a "spanner" that you can apply a couple to.

    that is my fear John.G!!!:eek: and why I might go down the nrv route


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    #60
    THE ALM
    Registered Users Posts: 1,596 ✭✭✭THE ALM


    Well, having woken to no heat a morning or two decided to revisit this sooner rather than later.

    Fairly mild day yesterday so decided to drain down the system and remove the nrv. Looks like nothing is moving inside but can't remove it from the isolator valve to have a proper inspection. Have replaced all with new so will see how we go over the next few days and hopefully that was the cause of my problems.


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    #61
    John.G
    Registered Users Posts: 3,466 ✭✭✭John.G


    THE ALM wrote: »
    Well, having woken to no heat a morning or two decided to revisit this sooner rather than later.

    Fairly mild day yesterday so decided to drain down the system and remove the nrv. Looks like nothing is moving inside but can't remove it from the isolator valve to have a proper inspection. Have replaced all with new so will see how we go over the next few days and hopefully that was the cause of my problems.

    I take it that you now have a new pump isolator valve & Poppet type NR valve fitted.
    If you pour water down the (removed) isolator valve end then water should flow/trickle out if the NRV is stuck partially open, if stuck shut or indeed working quite normally then no water might come out, I would just cut off the isolator valve to get a good view of that NRV because if the problem still persists then you still won't know where the problem lies.


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