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Child Item

High Limit Stat tripping

THE ALM

Hey all,

Hope somebody can give me some pointers.

Simple enough setup I would think. Warmflow Whitebird Utility boiler feeding two circulating pumps, one feeding radiators and the other feeding hot water cyclinder.

Can have the heating or heating & hot water on together but when just running hot water the high limit stat will trip.

Have replaced the two circulating pumps in the last couple of weeks which has made no difference, old ones where starting to make a bit of a noise so needed replacing anyway (13yrs running at this stage).

Pipe into cyclinder would be warm and pipe leaving cyclinder also warm. Would find that the hot water would be warm but never hot enough that I would need to mix with cold water.

Would also find that I could bleed some air from closest radiator, also in utility room, regularly enough in case this has any bearing.

Any advice appreciated.

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jimf

jc500 wrote: »

Would have thought control stat should operate before limit stat. Solid fuel furnace boilers have issues with too much oxygen in combustion and too much heat causing limit stat on fan to trip. Excessive heat in water jacket after pump stops. Maybe just water pump fault.

as a rule control stat will operate before limit stat

but if control goes faulty and doesn't trip at set temp then limit stat should lock boiler to safe mode

jc500

Would have thought control stat should operate before limit stat. Solid fuel furnace boilers have issues with too much oxygen in combustion and too much heat causing limit stat on fan to trip. Excessive heat in water jacket after pump stops. Maybe just water pump fault.

John.G

THE ALM wrote: »

Think so jimf

THE ALM wrote: »

Actually thinking about this a bit more and the Delta T for the HW would be dependant on the temp of the water in the cylinder at the time would it not?

If the water already in the tank is close to that passing through it then there is going to be little of no transfer of heat and the return temp is going to be only marginally lower than the flow temp. A more accurate Delta T reading would be from running it when the cylinder is at a much lower temp.

At the moment I measure the temp of the cyclinder through a smartthings sensor so I must measure the temp of water coming from a tap to see how accurate this sensor is and adjust accordingly.

It's the deltaT across the boiler that I am interested in, this is only dependant on two items, the boiler output and the flowrate, it doesn't matter what the heat load is. The heat load determines the boiler run time.

THE ALM

jimf wrote: »

last comment on this post from me

do ye not think at this stage lads overthinking is really kicking in

Think so jimf

jimf

last comment on this post from me

do ye not think at this stage lads overthinking is really kicking in

THE ALM

Actually thinking about this a bit more and the Delta T for the HW would be dependant on the temp of the water in the cylinder at the time would it not?

If the water already in the tank is close to that passing through it then there is going to be little of no transfer of heat and the return temp is going to be only marginally lower than the flow temp. A more accurate Delta T reading would be from running it when the cylinder is at a much lower temp.

At the moment I measure the temp of the cyclinder through a smartthings sensor so I must measure the temp of water coming from a tap to see how accurate this sensor is and adjust accordingly.

THE ALM

John.G wrote: »

Thanks for that, what I find difficult to understand is the very small deferential across the boiler while firing, my own 20 kw boiler has a measured delta t of - 24C which equates to a flow rate of 12 LPM, the coil delta t is - 6Cwhich means the boiler average output required is - 25 p.cent resulting in frequent boiler cycling..... Quite normal. In your case the boiler delta t averages 5.7C which assuming a 25 kw boiler equates to a flow rate of 62 LPM, highly unlikely and it also means that the cyl coil can absorb 25 kw again unlikely, the only other explanation that I can think of is that your boiler is cycling on/off very very often??

Thanks for that John.G.

I don't believe the boiler is cycling very very often, must compare when running heating only.

With the above figures in mind there is either a coil very encrusted in limescale and not dissipating heat, 15 year old in a moderate to high limescale area, or the pump is running to high so I'll turn that down this evening and see if that helps.

John.G

THE ALM wrote: »

Just coming back to you on this John.G - Took a couple of readings this morning which are:-

Flow 66.5 Return 61.6
Flow 65.2 Return 58.8
Flow 64.6 Return 58.7

Thanks for that, what I find difficult to understand is the very small deferential across the boiler while firing, my own 20 kw boiler has a measured delta t of - 24C which equates to a flow rate of 12 LPM, the coil delta t is - 6Cwhich means the boiler average output required is - 25 p.cent resulting in frequent boiler cycling..... Quite normal. In your case the boiler delta t averages 5.7C which assuming a 25 kw boiler equates to a flow rate of 62 LPM, highly unlikely and it also means that the cyl coil can absorb 25 kw again unlikely, the only other explanation that I can think of is that your boiler is cycling on/off very very often??

THE ALM

John.G wrote: »

Glad you are sorted, I would be very interested in the boiler flow & return temperature when it's firing on HW only, if you get a chance.

Just coming back to you on this John.G - Took a couple of readings this morning which are:-

Flow 66.5 Return 61.6
Flow 65.2 Return 58.8
Flow 64.6 Return 58.7

jimf

should be fine at 65/70

THE ALM

jimf wrote: »

I think they are 1 to 5 settings on those stats

set to 4 at max

not even that on this one just a general scale type image. Settings on manual state from 50 - 80° and I have it set about the 60-65° mark.

jimf

I think they are 1 to 5 settings on those stats

set to 4 at max

jimf

hopefully you are sorted everything crossed

THE ALM

No problem John.G, will get a look at that over the weekend.

John.G

THE ALM wrote: »

New stat fitted and no trips last night and came on this morning as expected, who would have thought :rolleyes::) Hopefully continues now uninterrupted and was the cause of the problems.

Glad I carried out the other work anyway as new valves were needed and it gave me the chance to change a radiator and learn a few new things along the way. As mentioned earlier, house much more evenly heated as a couple of rooms were always on the cooler side and feels like it's running more efficiently and as it should.

Will monitor and take a few readings over the weekend but so far so good.

Again, thanks for all the help, appreciated.[/

Glad you are sorted, I would be very interested in the boiler flow & return temperature when it's firing on HW only, if you get a chance.

THE ALM

New stat fitted and no trips last night and came on this morning as expected, who would have thought :rolleyes::) Hopefully continues now uninterrupted and was the cause of the problems.

Glad I carried out the other work anyway as new valves were needed and it gave me the chance to change a radiator and learn a few new things along the way. As mentioned earlier, house much more evenly heated as a couple of rooms were always on the cooler side and feels like it's running more efficiently and as it should.

Will monitor and take a few readings over the weekend but so far so good.

Again, thanks for all the help, appreciated.

THE ALM

jimf wrote: »

as stated in November and January

warmflow stats are known for intermittent problems

ie nuisance tripping of hl stat once a month for a while then getting more frequent until it happens constantly

sounds about right! hopefully new stat sorts out problem.

THE ALM

agusta wrote: »

Reread your post,it may be intermittent.Earlier you said it never cuts out on run stat.We can only go with what you say.This post says it does cut out on run stat if you adjust it

sorry, should have been phrased more as question, will edit accordingly.

Have someone collecting the new stat for me this evening, don't want to run into major problems!!

jimf

as stated in November and January

warmflow stats are known for intermittent problems

ie nuisance tripping of hl stat once a month for a while then getting more frequent until it happens constantly

agusta

THE ALM wrote: »

It may be an intermittent problem with the boiler stat, if such a thing is possible, as I can adjust the boiler stat (1-5 setting) and it will go off or come on accordingly, otherwise what you are describing is pretty accurate.

Reread your post,it may be intermittent.Earlier you said it never cuts out on run stat.We can only go with what you say.This post says it does cut out on run stat if you adjust it

jimf

agusta wrote: »

Part of your training

you seem to forget adam and eves dog was a pup when I was training

:o:o

agusta

jimf wrote: »

whats this testing garbage you speak of :D

Part of your training

THE ALM

agusta wrote: »

4 months is not intermittent

fair point agusta, it has dragged on a bit longer that I would have liked due to some personal matters.

Thanks again for your input, it is appreciated.

jimf

agusta wrote: »

Ya,but do you test it after:)

whats this testing garbage you speak of

agusta

jimf wrote: »

very simple stat to change

even agusta could manage it :):)

Ya,but do you test it after:)

THE ALM

agusta wrote: »

its a faulty run stat as advised to check in previous posts
I wouldnt be running a boiler with a faulty run stat.if the safety hi limit stat failed it could do some damage.
if you dont know how a duel stat works,id advise to get a service technician to fit it for you.what looks simple is sometimes not that simple
The new stat fitted should be tested

Thanks agusta, a full service will be carried out as it is due anyway in the coming weeks.

THE ALM

jimf wrote: »

if im reading this correctly the only control over the run temp of the boiler is the room stat

by the time the room stat is satisfied the temp within the boiler is way above what it should be

the circulating pump is just about able to keep the boiler below high limit stat trip point

which then trips within mins because static water temp continues to rise within the boiler chamber

Edit : Could it may be an intermittent problem with the boiler stat, if such a thing is possible, as I can adjust the boiler stat (1-5 setting) and it will go off or come on accordingly, otherwise what you are describing is pretty accurate.

agusta

THE ALM wrote: »

Will take this reading as well, thanks John.G, happy enough that the bottom is the lower of the two as the flow direction was all double checked when changing the NRV on Tuesday.

Have checked with a local builders providers and they have the warmflow dual stat in stock and half the price I see quoted on line, so happy enough with that. Won't have a chance to fit until tomorrow night.

its a faulty run stat as advised to check in previous posts
I wouldnt be running a boiler with a faulty run stat.if the safety hi limit stat failed it could do some damage.
if you dont know how a duel stat works,id advise to get a service technician to fit it for you.what looks simple is sometimes not that simple
The new stat fitted should be tested

jimf

THE ALM wrote: »

Will take this reading as well, thanks John.G, happy enough that the bottom is the lower of the two as the flow direction was all double checked when changing the NRV on Tuesday.

Have checked with a local builders providers and they have the warmflow dual stat in stock and half the price I see quoted on line, so happy enough with that. Won't have a chance to fit until tomorrow night.

very simple stat to change

even agusta could manage it

:):)

THE ALM

John.G wrote: »

l

My last twopence worth try and get the flow & return boiler temperatures as a pretty good estimation of the flow rate can be calculated from this and also ensure that the bottom is the lower reading of the two to ensure that you havn,t reversed flow through the boiler ie top to bottom.

Will take this reading as well, thanks John.G, happy enough that the bottom is the lower of the two as the flow direction was all double checked when changing the NRV on Tuesday.

Have checked with a local builders providers and they have the warmflow dual stat in stock and half the price I see quoted on line, so happy enough with that. Won't have a chance to fit until tomorrow night.