High Limit Stat tripping

THE ALM · 13-12-2018 12:24pm

John.G wrote: »

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.

Well John.G indeed I have fitted all new, pouring water in either end will allow water to trickle though so it looked like it was stuck partially open.

I have just given it a few belts with a hammer which has loosed the joint so have managed to remove it and indeed this is the case. The spring loaded rubber closing disc has two 'pins' either side which should slide up and down inside the housing but both have sufficient limescale/grime to prevent this happening. For me to even get the disc out has required a few taps with a hammer so definitely not moving freely that is for sure.

Now, do I do the same on the heating pump side? Might leave that until the New Year!

John.G · 13-12-2018 12:46pm

THE ALM wrote: »

Well John.G indeed I have fitted all new, pouring water in either end will allow water to trickle though so it looked like it was stuck partially open.

I have just given it a few belts with a hammer which has loosed the joint so have managed to remove it and indeed this is the case. The spring loaded rubber closing disc has two 'pins' either side which should slide up and down inside the housing but both have sufficient limescale/grime to prevent this happening. For me to even get the disc out has required a few taps with a hammer so definitely not moving freely that is for sure.

Now, do I do the same on the heating pump side? Might leave that until the New Year!

That's good news that you found the guide pins sticking and hopefully now the boiler won't trip out on hot water zone only, the hot water cylinder should heat up faster as well which was the whole object of the exercise, eventually you may even be able to put that circ pump back on PP control.

If the rads are all heating OK then I would leave well enough alone but would certainly open it up and perhaps renew as above at your convenience, I would advise putting in some inhibitor ASAP if not all ready done so, if you havn't then you can wait until you drain the system down to inspect/renew that NRV.

I presume that you have that (rads) zone pump running on PP6 as well?.

THE ALM · 13-12-2018 1:42pm

John.G wrote: »

That's good news that you found the guide pins sticking and hopefully now the boiler won't trip out on hot water zone only, the hot water cylinder should heat up faster as well which was the whole object of the exercise, eventually you may even be able to put that circ pump back on PP control.

If the rads are all heating OK then I would leave well enough alone but would certainly open it up and perhaps renew as above at your convenience, I would advise putting in some inhibitor ASAP if not all ready done so, if you havn't then you can wait until you drain the system down to inspect/renew that NRV.

I presume that you have that (rads) zone pump running on PP6 as well?.

Here is hoping John.G. Rads heating ok so will leave it for now alright but will renew that side as well for peace of mind, running at PP6. Inhibitor added so all good there.

Thanks for all the advice and have a happy and peaceful Christmas.

THE ALM · 19-01-2019 11:30am

Just coming back to this, meant to a couple of weeks back, but unfortunately this has not cured my issue but in fact it seems to have exacerbated it.

Again, the heating and hot water are doing there job, have hot radiators and hot water. Have set both pumps to come on together with the heating then continuing to run after the hot water has stopped (no need to run the hot water on its own at this time of year). The heating will run its schedule no problem, can be 30mins or 2 hours, but at the end the high limit stat will have tripped and will need resetting.

My thinking now is that once the schedule has stopped and therefore the pumps are not running that the water in the boiler is continuing to heat from the residual heat of the boiler causing the trip.

Having replaced the NRV on the hot water side I plan on doing same on heating side to see if this has any bearing on it.

Another option could be a faulty dual stat and with that in mind would this dual stat work as well as the original as there is a considerable difference in price.

Thanks for any advice.

John.G · 19-01-2019 12:58pm

THE ALM wrote: »

Just coming back to this, meant to a couple of weeks back, but unfortunately this has not cured my issue but in fact it seems to have exacerbated it.

Again, the heating and hot water are doing there job, have hot radiators and hot water. Have set both pumps to come on together with the heating then continuing to run after the hot water has stopped (no need to run the hot water on its own at this time of year). The heating will run its schedule no problem, can be 30mins or 2 hours, but at the end the high limit stat will have tripped and will need resetting.

My thinking now is that once the schedule has stopped and therefore the pumps are not running that the water in the boiler is continuing to heat from the residual heat of the boiler causing the trip.

Having replaced the NRV on the hot water side I plan on doing same on heating side to see if this has any bearing on it.

Another option could be a faulty dual stat and with that in mind would this dual stat work as well as the original as there is a considerable difference in price.

Thanks for any advice.

Just to be clear on this part of it first, original problem was HL stat tripping on HW only + very slow cylinder heat up time. HW side only NR valve only replaced. NOW if you run HW side ONLY, (1) Is the HL stat still tripping? and (2) is the cylinder heat up time faster, you say above that it is getting hot?.

John.G · 19-01-2019 1:39pm

John.G wrote: »

Just to be clear on this part of it first, original problem was HL stat tripping on HW only + very slow cylinder heat up time. HW side only NR valve replaced. NOW if you run HW side ONLY, (1) Is the HL stat still tripping? and (2) is the cylinder heat up time faster, you say above that it is getting hot?.

EDIT: In your very first post you said "Can have the heating or heating & hot water on together but when just running hot water the high limit stat will trip." So this implies that there wasn't a problem with heating only on then? I assume that you were then and are now running the heating pump on PP6.
Now if the HL stat isn't tripping now on/after HW only on then it would seem logical to renew the heating NR.

THE ALM · 19-01-2019 1:46pm

John.G wrote: »

Just to be clear on this part of it first, original problem was HL stat tripping on HW only + very slow cylinder heat up time. HW side only NR valve only replaced. NOW if you run HW side ONLY, (1) Is the HL stat still tripping? and (2) is the cylinder heat up time faster, you say above that it is getting hot?.

Hi John.G

The HW only will still trip the HL stat and the hot water does heat up quicker, never timed it but appears to but may not necessarily be the case. Certainly getting hotter water than previously.

I could run the heating for 90mins with the hot water running in parallel for the first 30mins of those 90, no problems there. Could then shut off as normal but when heat is called for again the HL stat has tripped.

HW side only NRV has been replaced.

EDIT: Not sure that I have run the heating only since replacing the HW NRV so will try that this evening to see what results I get.

THE ALM · 19-01-2019 2:04pm

What I do find now is that the HL stat will trip after almost all instances of heating and hot water being on e.g:-

Heating and HW both on in the morning for 30mins - Stat tripped after

18:15-20:30 Heating & 18:30-19:45 HW - May not run the full time as house may have reached set temp and turned heat off - Stat tripped after schedule

21:30-22:30 heating only - Again, may not run for full hour if temp reached - stat tripped.

Can ignore the edit on the last post as, looking at the heating schedule, I do obviously run the heating only.

John.G · 19-01-2019 2:48pm

THE ALM wrote: »

What I do find now is that the HL stat will trip after almost all instances of heating and hot water being on e.g:-

Heating and HW both on in the morning for 30mins - Stat tripped after

18:15-20:30 Heating & 18:30-19:45 HW - May not run the full time as house may have reached set temp and turned heat off - Stat tripped after schedule

21:30-22:30 heating only - Again, may not run for full hour if temp reached - stat tripped.

Can ignore the edit on the last post as, looking at the heating schedule, I do obviously run the heating only.

Strange alright as originally (last oct/nov) you said it didn't trip on heating only? It may point to a faulty boiler stat, If you still can get a hold of that temperature scanner you could check the boiler flow temperature on cut out and keep checking it for a few minutes after to see does it keep climbing, if the temperature is in fact reaching 110/115C HL cut out I would think that you would hear a bit of gurgling sounds if standing at the boiler. Failing that you could get someone in with the appropriate "Fluke" which I think has a thin sensor that can be inserted in the boiler pocket with the other two sensors still inside, or you could just replace the complete combined stat, hard to advise on what to do really but I would certainly go the scanner route initially if easily obtainable.
I presume the boiler has been serviced relatively recently and that the furnace isn't covered in oily soot which would give after burning with burner shutdown, unlikely I would think if burning Kero.

THE ALM · 19-01-2019 4:01pm

Thanks again John.G, will do a bit more investigating and see how temperatures are, failing anything obvious it could be time to call someone out.

Will change the NRV on the heating side while I'm at it.

John.G · 22-01-2019 10:33pm

THE ALM wrote: »

Thanks again John.G, will do a bit more investigating and see how temperatures are, failing anything obvious it could be time to call someone out.

Will change the NRV on the heating side while I'm at it.

Just thinking there again, I know this sounds a bit daft/improbable but are you sure that both pumps and NR valves are installed correctly IE, both pumps pumping downwards and arrows on NRV's pointing downwards, its a bit strange that the flow through the cylinder coil is bottom to top, that's what prompted this. Of course if the NR valves were/are installed correctly and one pump was installed incorrectly then there should be no flow through that particular circuit as the NRV should close....I know the temperatures shown in the attachment in #50 would indicate that the circulation is correct but worth having a quick look anyway.

A neighbour of mine had a problem with his hi limit stat tripping out occasionally, I had a look at it one day and found the pump pumping the wrong way and had been doing so for around 5 years (but the pump label was the right way up!)

THE ALM · 24-01-2019 1:49pm

John.G wrote: »

Just thinking there again, I know this sounds a bit daft/improbable but are you sure that both pumps and NR valves are installed correctly IE, both pumps pumping downwards and arrows on NRV's pointing downwards, its a bit strange that the flow through the cylinder coil is bottom to top, that's what prompted this. Of course if the NR valves were/are installed correctly and one pump was installed incorrectly then there should be no flow through that particular circuit as the NRV should close....I know the temperatures shown in the attachment in #50 would indicate that the circulation is correct but worth having a quick look anyway.

A neighbour of mine had a problem with his hi limit stat tripping out occasionally, I had a look at it one day and found the pump pumping the wrong way and had been doing so for around 5 years (but the pump label was the right way up!)

I am pretty confident that they are installed and pumping correctly in the right direction but certainly something that I will double check.

Was away for a few days and it is a bit of a nuisance to come back to a cold house.

Hopefully in the coming week I'll get the other NRV replaced.

One other thing I did notice the other morning is that the overflow from the F&E tank was overflowing. Haven't had time to investigate this as I was away so wondering does this point to anything in particular. Not the ballcock so have to check if it is coming from the feed or vent pipe. Have lowered the settings on the pump to see if this has any affect also.

jimf · 24-01-2019 5:35pm

pump would be the first thing to rule out

intermittent problems with pumps is also not unheard of might explain the hl stat as well

John.G · 24-01-2019 5:48pm

jimf wrote: »

pump would be the first thing to rule out

intermittent problems with pumps is also not unheard of might explain the hl stat as well

A possibility but both pumps were renewed ~ Oct 2018 so unlikely?, the deltaT across the boiler can be measured with the scanner and that will tell a lot, IMO 15/25C might be expected with CH on and maybe 5/10C on HW only.

Correction, on HW only 5/10C maybe expected across coil and 20/30C across boiler.

THE ALM · 24-01-2019 5:49pm

jimf wrote: »

pump would be the first thing to rule out

intermittent problems with pumps is also not unheard of might explain the hl stat as well

Thanks jimf. Two new pumps, but again will check both.

agusta · 25-01-2019 7:54pm

Why would you change pumps and non return valve without first checking at what temp is the hi-limit tripping at.this is the first port of call.a simple temp probe would give you this information

THE ALM · 30-01-2019 10:10pm

Well have had heating running as usual this evening for about two hours until thermostat temp was reached, 19°. Waited 5-10 mins and checked HL stat to see it had tripped, checked with temp probe in stat pocket to read 101°

jimf · 30-01-2019 10:14pm

the usual hl stat trip temp is about 112 dg plus or minus 5%

THE ALM · 30-01-2019 10:44pm

jimf wrote: »

the usual hl stat trip temp is about 112 dg plus or minus 5%

Will take a few more readings to confirm and see how they go.

jimf · 30-01-2019 10:54pm

this post is running so long I cant remember if the stat on the boiler is new or old

2 scenarios run stat not cutting out at set temp or hl stat tripping at lower than usual trip temp

THE ALM · 31-01-2019 11:11am

jimf wrote: »

this post is running so long I cant remember if the stat on the boiler is new or old

2 scenarios run stat not cutting out at set temp or hl stat tripping at lower than usual trip temp

you are right there jimf

Not a new stat so that, I imagine, is my next port of call as now both pumps are replaced and new valves to both fitted, these needed doing so no loss there.

Spent a bit of time balancing out the system yesterday evening as I noticed a couple of rads weren't fulling heating, more consistent temperature throughout house now.

As asked earlier would this dual stat work as well as the original as there is a considerable difference in price.

John.G · 31-01-2019 11:27am

THE ALM wrote: »

Well have had heating running as usual this evening for about two hours until thermostat temp was reached, 19°. Waited 5-10 mins and checked HL stat to see it had tripped, checked with temp probe in stat pocket to read 101°

Main item to check is the boiler stat cut out point, sit in front of the boiler with the probe inserted in pocket and check the temperature when the burner cuts out(room stat still calling) if burner cuts out at say 75C (mid scale on boiler stat setting dial) and the boiler temp then rises to 101C then you know that the problem isn,t the boiler stat. Two queries: did the boiler trip out/fail to restart @101C & have you renewed the ch NRV.
Edit: I see you have replaced the NRV so be sure you check that boiler stat cut out above before any change out, also suggest pump c/o to fixed speed maybe 2 but ensure F&E tank not overflowing. I know the PP6 setting should be fine but I still suspect that you have a low flow circulation problem.0

THE ALM · 31-01-2019 12:04pm

John.G wrote: »

Main item to check is the boiler stat cut out point, sit in front of the boiler with the probe inserted in pocket and check the temperature when the burner cuts out(room stat still calling) if burner cuts out at say 75C (mid scale on boiler stat setting dial) and the boiler temp then rises to 101C then you know that the problem isn,t the boiler stat. Two queries: did the boiler trip out/fail to restart @101C & have you renewed the ch NRV.

Will check that out this evening. CH NRV has been replaced.

Just to reiterate, when the room stat is calling heat there is no issue, boiler and pump comes on, radiators heat and when temperature reached the boiler and pumps turn off. At no point, if heat is being called, will the boiler cut out whether it takes 45 or 90 mins to reach room stat temp. Listening to the boiler running (utility room), in whatever time it takes to reach room stat temp, I can hear it cut in and out and therefore would assume that the boiler stat is working as it should - boiler and pump come on, boiler heats water, boiler reaches boiler stat temp and turns off, pump keeps running and water temp gradually drops, boiler stat temp drops and boiler fires up again, cycle continues until room stat temp reached and both boiler and pump turn off.

This morning e.g. the heating comes on for 30mins, generally won't hit the room stat temperature in those 30mins before it turns off as normal and as I would expect. Got up to find HL tripped.

agusta · 31-01-2019 2:21pm

THE ALM wrote: »

Well have had heating running as usual this evening for about two hours until thermostat temp was reached, 19°. Waited 5-10 mins and checked HL stat to see it had tripped, checked with temp probe in stat pocket to read 101°

This still tells you nothing.
Set The run stat to 70,insert temp probe in boiler.

1/What temp in probe do you get when boiler first cuts out on temp?
2/When boiler first cuts on temp, turn off time clock or turn down the room stat to zero.what does the temp probe rise to?
If you cant get an answer to the above 2 ,it only guesswork

THE ALM · 31-01-2019 3:28pm

agusta wrote: »

This still tells you nothing.
Set The run stat to 70,insert temp probe in boiler.

1/What temp in probe do you get when boiler first cuts out on temp?
2/When boiler first cuts on temp, turn off time clock or turn down the room stat to zero.what does the temp probe rise to?
If you cant get an answer to the above 2 ,it only guesswork

Thanks agusta will check that this evening. As said, the boiler won't cut out on temp only, when finished running will the HL stat trip.

I'll take a reading when boiler is running and see if it is within the boiler stat parameters and another reading when finished running to see what temp it reaches.

Appreciate all the help all.

jimf · 31-01-2019 3:38pm

are you actually saying the boiler wont cut out on the run stat regardless off how long its running ????

jimf · 31-01-2019 3:40pm

THE ALM wrote: »

you are right there jimf

Not a new stat so that, I imagine, is my next port of call as now both pumps are replaced and new valves to both fitted, these needed doing so no loss there.

Spent a bit of time balancing out the system yesterday evening as I noticed a couple of rads weren't fulling heating, more consistent temperature throughout house now.

As asked earlier would this dual stat work as well as the original as there is a considerable difference in price.

once the phials from the stat fit in the pocket yes

wiring will be different but no major issue

agusta · 31-01-2019 3:50pm

THE ALM wrote: »

Thanks agusta will check that this evening. As said, the boiler won't cut out on temp only, when finished running will the HL stat trip.

I'll take a reading when boiler is running and see if it is within the boiler stat parameters and another reading when finished running to see what temp it reaches.

Appreciate all the help all.

No, two exact answers are required with 1 degree to the two questions i asked in post 85!.The burner is not running when you take the two measurements.And
the pump is def not running for the second question
It has not been mentioned previously that the boiler wont cut out on temp

THE ALM · 31-01-2019 3:52pm

jimf wrote: »

are you actually saying the boiler wont cut out on the run stat regardless off how long its running ????

Correct

jimf · 31-01-2019 3:59pm

then change stat before you go any further

as advised earlier on this thread warmflow stats are known for intermittent problems

see post 34 dated 4th November

High Limit Stat tripping

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