Keep the circulating pump running for 2-3 mins after boiler shuts off

Blowheads

Afternoon,
We have a 3 zone system, Water on a normal time clock, upstairs and downstairs on 2 Nest Stats.
The (outdoor oil) boiler is regularly tripping out the high temp stat, which results in having to go out, reset the little button and away we go until the next time.
What I think is happening, the call for water comes from any zone, pump and boiler kick on and when stat stops the call BOTH the boiler and circulating pump stops, I believe that the water in the boiler is still heating due to residual heat, overheats the boiler stat and trips out the high temp stat.
There is a bypass on the water circle so is no issues to run the pump
So.. how to get the circulating pump to run for 2-5 mins AFTER the boiler has stopped, thereby cooling down the water in the boiler a little. I understand not to leave the pump running full time because it will take all the cold from the tank
Any suggestions?
Thanks!

John.G

Blowheads wrote: »

Afternoon,
We have a 3 zone system, Water on a normal time clock, upstairs and downstairs on 2 Nest Stats.
The (outdoor oil) boiler is regularly tripping out the high temp stat, which results in having to go out, reset the little button and away we go until the next time.
What I think is happening, the call for water comes from any zone, pump and boiler kick on and when stat stops the call BOTH the boiler and circulating pump stops, I believe that the water in the boiler is still heating due to residual heat, overheats the boiler stat and trips out the high temp stat.
There is a bypass on the water circle so is no issues to run the pump
So.. how to get the circulating pump to run for 2-5 mins AFTER the boiler has stopped, thereby cooling down the water in the boiler a little. I understand not to leave the pump running full time because it will take all the cold from the tank
Any suggestions?
Thanks!

Oil boilers are usually installed with no pump over run at shut down.
The water content of oil boilers is normally 20 to 30 litres so that volume of water can usually absorb enough residual heat so that the hi level temperature stat doesn't operate.
The hi level stat should not operate until the temperature reaches 110C to 115C.
If the boiler stat is set very high then on shutdown the hi level stat may operate.
What temperature setting have you the boiler stat set at?.
Has this only happened recently since replacing a circulating pump or something else.?
You may have a faulty boiler stat or Hi limit stat.

Blowheads

John.G wrote: »

Oil boilers are usually installed with no pump over run at shut down.
The water content of oil boilers is normally 20 to 30 litres so that volume of water can usually absorb enough residual heat so that the hi level temperature stat doesn't operate.
The hi level stat should not operate until the temperature reaches 110C to 115C.
If the boiler stat is set very high then on shutdown the hi level stat may operate.
What temperature setting have you the boiler stat set at?.
Has this only happened recently since replacing a circulating pump or something else.?
You may have a faulty boiler stat or Hi limit stat.

Hi,
Boiler stat is set to 65-70. No new pump or other components installed. This used to happen a bit a few years ago and I replaced the boiler stat twice to see it that was that..a new one would be the 3rd...

Wearb

OP: Do you have anyway of measuring the temperature in the temperature probe pocket? It would be useful to have information on cut-out temperature on boiler stat and on hi-limit stat, when each of them operates. It would at least let you know if either of them are faulty.

Blowheads

Wearb wrote: »

OP: Do you have anyway of measuring the temperature in the temperature probe pocket? It would be useful to have information on cut-out temperature on boiler stat and on hi-limit stat, when each of them operates. It would at least let you know if either of them are faulty.

Boiler stat seems to be working fine, in that if you turn it up or down she will call for heat or not. I don't know how you could probe the probe, would need something to monitor that in real time and also from remote so not to be sitting outside at it, also the fact the high stat trips randomly it would need to be constantly monitored up to the point of the trip out

Wearb

Blowheads wrote: »

Boiler stat seems to be working fine, in that if you turn it up or down she will call for heat or not. I don't know how you could probe the probe, would need something to monitor that in real time and also from remote so not to be sitting outside at it, also the fact the high stat trips randomly it would need to be constantly monitored up to the point of the trip out

Most multimeters would have the ability to do such measurements. You could easily set up your heating to have the boiler stat active quickly, similar for hi limit stat.
Running the pump for a few minutes through the bypass without a zone open, might not prevent the hi limit stat operating

John.G

Blowheads wrote: »

Boiler stat seems to be working fine, in that if you turn it up or down she will call for heat or not. I don't know how you could probe the probe, would need something to monitor that in real time and also from remote so not to be sitting outside at it, also the fact the high stat trips randomly it would need to be constantly monitored up to the point of the trip out

Two other things come to mind, the first one is are you sure that the burner is switched off at the same time as the circ pump?, its just possible that the circ pump is stopping as per programmer/timer but the burner continues to fire until the boiler stat stops it, this would certainly make it more prone then to reach the hi limit stat temperature as well.
I have personal knowledge of the other event which happened to a neighbour of mine..... he would find his boiler "out" on the hi limit stat regularly in the morning when the boiler was timed to come on. He mentioned this to me on a few occasions and told me that this problem had started when he had the circ pump renewed around 3 to 4 years previously. I finally had a look and found that the circ pump which was installed in the flow from the boiler was pumping the wrong way, ie pumping the water downwards through the boiler ( non condensing Firebird), he got the pump reversed and that was the end of his problem. So even though unlikely, check the direction of flow, (arrow on pump body), if the pump is installed in the Flow side of the boiler then the arrow should point away from the boiler, if installed on the Boiler return then the arrow should point into the boiler.

jimf

do you have a stove or a back boiler heating rads etc on the same system

is the boiler a standard efficiency firebird boiler by chance

agusta

Blowheads wrote: »

Boiler stat seems to be working fine, in that if you turn it up or down she will call for heat or not. I don't know how you could probe the probe, would need something to monitor that in real time and also from remote so not to be sitting outside at it, also the fact the high stat trips randomly it would need to be constantly monitored up to the point of the trip out

You can just put a probe on the flow pipe on top of the boiler.if run stat is set to 65 ,then when the pipe reaches 65 approx the burner should stop.If your run stat is faulty, it may not be turning off the burner until it reaches 85 even though its set to 65,

John.G

agusta wrote: »

You can just put a probe on the flow pipe on top of the boiler.if run stat is set to 65 ,then when the pipe reaches 65 approx the burner should stop.If your run stat is faulty, it may not be turning off the burner until it reaches 85 even though its set to 65,

Don't want to be muddying the waters but both the Firebird SE and the Enviromax manuals state that a over run thermostat may be fitted in cases "where the boiler return is downwards", in the case of the enviromax, the manual actually shows a over run thermostat set at 87C and states that Firebird supplies them. If the by pass valve is located as far as possible from the boiler then that loop alone should dissipate the heat even with zoning, I think gas boilers actually have that by pass fitted inside in the boiler enclosure.

Should mention that I have a Firebird SE 90s boiler myself for the past 13 years and it has never tripped out the hi limit stat (only it did once a few weeks ago when I fired it up with the circ pump disabled as a test on some other thread here).

jimf

don't know how old your boiler is but firebird had a batch of problem stats a few years back

they presented with intermittent tripping of hl stat and excess heat from the run stat

but you stated you have changed your stat a few times so not likely in your case

Blowheads

I'll check the pump direction tomorrow but I'm assuming it's in the right direction given the plumber had his nose in it Saturday
As I recall the boiler and pump both stopped when the call for heat stopped and the boiler always stops when call for heat stops
Double check tomorrow in fair light and weather..

Blowheads

What temperature should the high stat trip at?
Above said 110-115? Would the water not be boiling mad inside at that stage?

Blowheads

jimf wrote: »

do you have a stove or a back boiler heating rads etc on the same system

is the boiler a standard efficiency firebird boiler by chance

Yes a wet stove, but it tripped independent of the stove lit and tripped even when the stove is not hot

agusta

Blowheads wrote: »

What temperature should the high stat trip at?
Above said 110-115? Would the water not be boiling mad inside at that stage?

yes,the first check is to test the run stat

John.G

Blowheads wrote: »

What temperature should the high stat trip at?
Above said 110-115? Would the water not be boiling mad inside at that stage?

With a gravity fed system one would certainly be aware of it if standing at the boiler, see post 14 of this thread, https://www.boards.ie/vbulletin/showthread.php?t=2057909689

With gravity fed system and boiler on ground floor of 3 storey house then you would have a head pressure of 0.5 to 0.6 bar which = boiling point of 112C/114C.
With a sealed system running between 1 bar and 2 bar the boiling points are 120C @ 1 bar, 125C @ 1.5 bar & 133C @ 2 bar so you may hear very little in this case.

What Boiler make have you installed and is it condensing (HE) or non condensing (SE)?.

jimf

nuisance trips are probably the worst thing to encounter with boilers


you could spend hours and still not get to the bottom of it

agusta

jimf wrote: »

nuisance trips are probably the worst thing to encounter with boilers


you could spend hours and still not get to the bottom of it

One a year is enough..,Even if your on the hourly rate:)

John.G

Wearb wrote: »

Most multimeters would have the ability to do such measurements. You could easily set up your heating to have the boiler stat active quickly, similar for hi limit stat.
Running the pump for a few minutes through the bypass without a zone open, might not prevent the hi limit stat operating

Is there any such thing as a pipe (strap on) thermometer with a indicating needle that the temperature gauge pointer pushes up ahead of it?, this would then "record" the maximum temperature reached, it would be a handy tool to have. I presume the Fluke digital one can record this but it might have to be left in place for days on end thus tying up its use on some other job.

Wearb

John.G wrote: »

Is there any such thing as a pipe (strap on) thermometer with a indicating needle that the temperature gauge pointer pushes up ahead of it?, this would then "record" the maximum temperature reached, it would be a handy tool to have. I presume the Fluke digital one can record this but it might have to be left in place for days on end thus tying up its use on some other job.

I used a cheap Aldi/Lidl indoor/outdoor thermometer to diagnose a nusance fire valve trip. It has a min and max reading. This image looks a little like it but not the same one.

John.G

Wearb wrote: »

I used a cheap Aldi/Lidl indoor/outdoor thermometer to diagnose a nusance fire valve trip. It has a min and max reading. This image looks a little like it but not the same one.

I have a number of these sort (Lidl, Silvercrest) myself but they only read to a max of 70C (so they state) and the plastic outside sensor is quite bulky/akward for attachment to a pipe.

Wearb

John.G wrote: »

I have a number of these sort (Lidl, Silvercrest) myself but they only read to a max of 70C (so they state) and the plastic outside sensor is quite bulky/akward for attachment to a pipe.

Mine was a silvercrest one also. I didn't know what the max possible reading was. It was perfect for my purpose. Could also have the display outside the casing and watch in real time as the temperature in the casing continued to rise a little after shutdown. But not enough to cause the FV to activate.



There might be similar items available that can read higher than 100C. I never looked, as the scenarios in this case (OP) can be made to happen within a reasonably short time.



Sometime (maybe next spring), I must check to see if there is a considerable lag between temperature and either stat activating.

Blowheads

Ok here is this evenings findings,
1. The pump runs only when there is a call for heat from indoor stat. Turn off the stat, the pump stops

2. As best I can determine when the internal stat IS calling for heat, and I let the boiler run warm, and I then turn down the boiler stat then the pump also stops. Can't be 100% sure as the pump itself is hot

3. As I understand the return water pipe is at the bottom (cooler than the one at top) then the pump is plumbed the right direction, as in it pumps cold water into the boiler

See also pictures of the boiler ratings Grant 90/120

whizbang

It maybe a case of the Pump is not starting up everytime when the burner fires.
Is there any sludge in the system ? Undo the bleed screw and catch the water in a glass jar to see.

Is the pump itself overheating and shutting itself off ?

Re temps:
I have digital sensors on the outlet pipe about 100mm from the boiler outlet, and in the stat port.
When the pump is running these 2 temps are usually within 3degrees of each other, mostly depending on firing or not. When the boiler fires from cold, the outlet temp lags by up to 10deg, and very quickly catches up once the pump starts. (Pump on separate control). If the pump is off, the hotter the boiler gets, the less the temperature difference.

Blowheads

whizbang wrote: »

It maybe a case of the Pump is not starting up everytime when the burner fires.
Is there any sludge in the system ? Undo the bleed screw and catch the water in a glass jar to see.

Is the pump itself overheating and shutting itself off ?

Re temps:
I have digital sensors on the outlet pipe about 100mm from the boiler outlet, and in the stat port.
When the pump is running these 2 temps are usually within 3degrees of each other, mostly depending on firing or not. When the boiler fires from cold, the outlet temp lags by up to 10deg, and very quickly catches up once the pump starts. (Pump on separate control). If the pump is off, the hotter the boiler gets, the less the temperature difference.

What temperature gauge are you using?

whizbang

Is there an auto air bleed valve there leaking.?
Are you getting airlocks in the pump or boiler..

what speed is pump set to?

jimf

very unlikely the stat at the boiler has any control over the pump

whizbang

DS18S20. Using a PIC to control temps and pump. But got a Tado recently and haven't figured out how to control water temps.

John.G

Blowheads wrote: »

Ok here is this evenings findings,
1. The pump runs only when there is a call for heat from indoor stat. Turn off the stat, the pump stops

2. As best I can determine when the internal stat IS calling for heat, and I let the boiler run warm, and I then turn down the boiler stat then the pump also stops. Can't be 100% sure as the pump itself is hot

3. As I understand the return water pipe is at the bottom (cooler than the one at top) then the pump is plumbed the right direction, as in it pumps cold water into the boiler

See also pictures of the boiler ratings Grant 90/120

Point 3 verifies that circulation is correct.

Point 1 is also correct as power is supplied to both the circ pump and the boiler burner, the pump should continue to run continuously until the room stat is satisfied...then both pump and boiler burner should cut out. BUT regarding point 2, the circ pump should not cut out when the boiler burner cuts out, apart from anything else it will give poor radiator heating performance as the boiler could be off for a very long period as no heat is being transferred anywhere.

Edit: I came across another bit of test info re my own boiler, when the boiler cuts out normally on its stat at 75C and if I stop the circ pump immediately then the boiler water temperature rose another 10C to 12C...from 75C to 85C/87C.

John.G

whizbang wrote: »

It maybe a case of the Pump is not starting up everytime when the burner fires.
Is there any sludge in the system ? Undo the bleed screw and catch the water in a glass jar to see.

Is the pump itself overheating and shutting itself off ?

Re temps:
I have digital sensors on the outlet pipe about 100mm from the boiler outlet, and in the stat port.
When the pump is running these 2 temps are usually within 3degrees of each other, mostly depending on firing or not. When the boiler fires from cold, the outlet temp lags by up to 10deg, and very quickly catches up once the pump starts. (Pump on separate control). If the pump is off, the hotter the boiler gets, the less the temperature difference.

That point re pump and boiler burner on separate controls is interesting, does this mean so that the boiler is on "standby" even if no heat/hot water demand and will just cut in and out based on boiler stat?.

whizbang

Burner main control was house thermostats, Tado is set to relay only, so no water control anymore. Pump control based on flow/return temps.

agusta

Blowheads wrote: »

Ok here is this evenings findings,
1. The pump runs only when there is a call for heat from indoor stat. Turn off the stat, the pump stops

2. As best I can determine when the internal stat IS calling for heat, and I let the boiler run warm, and I then turn down the boiler stat then the pump also stops. Can't be 100% sure as the pump itself is hot

3. As I understand the return water pipe is at the bottom (cooler than the one at top) then the pump is plumbed the right direction, as in it pumps cold water into the boiler

See also pictures of the boiler ratings Grant 90/120

In picture 3,the two riello hoses needs to be changed...,Do you have a back boiler or boiler stove also.

Blowheads

agusta wrote: »

In picture 3,the two riello hoses needs to be changed...,Do you have a back boiler or boiler stove also.

Why those hoses need to be changed?

Yes a multifuel boiler stove, but as said the high stat can trip even when the stove is not lit

jimf

Blowheads wrote: »

Why those hoses need to be changed?

Yes a multifuel boiler stove, but as said the high stat can trip even when the stove is not lit

hoses clearly past their bf date

dull colour and rust etc is a giveaway

Blowheads

John.G wrote: »

Point 3 verifies that circulation is correct.

Point 1 is also correct as power is supplied to both the circ pump and the boiler burner, the pump should continue to run continuously until the room stat is satisfied...then both pump and boiler burner should cut out. BUT regarding point 2, the circ pump should not cut out when the boiler burner cuts out, apart from anything else it will give poor radiator heating performance as the boiler could be off for a very long period as no heat is being transferred anywhere.

Edit: I came across another bit of test info re my own boiler, when the boiler cuts out normally on its stat at 75C and if I stop the circ pump immediately then the boiler water temperature rose another 10C to 12C...from 75C to 85C/87C.

So you are saying, so long as the internal stat is calling for heat, the pump should be running?
I'll have to get a stethoscope or something as I can't judge when the boiler is running and the pump is hot..

agusta

There is a date on the hoses and they are along time out of date.The hoses are rubber and rubber perishes with time.They should be changed every couple of years.

Wearb

Blowheads wrote: »

Why those hoses need to be changed?

Yes a multifuel boiler stove, but as said the high stat can trip even when the stove is not lit

I have seen a situation where a boiler stove could be out for hours, but when oil boiler is turned the water from stove tripped the hi limit stat on oil boiler. It had some weird plumbing.

whizbang

So you are saying, so long as the internal stat is calling for heat, the pump should be running?
I'll have to get a stethoscope or something as I can't judge when the boiler is running and the pump is hot..

Yes.
undo the center screw on the back of pump, there may not be much water flow, you can see if the pump is running.

Worth replacing the motor capacitor anyway. they are normally reliable, but I dont know about this pump, and they dont cost much.

agusta

Blowheads wrote: »

Why those hoses need to be changed?

Yes a multifuel boiler stove, but as said the high stat can trip even when the stove is not lit

What is the stat set to on the multifuel stove?

Blowheads

agusta wrote: »

Blowheads wrote: »

Why those hoses need to be changed?

Yes a multifuel boiler stove, but as said the high stat can trip even when the stove is not lit

What is the stat set to on the multifuel stove?

the pipe stat for the boiler stove is set to 55-60

John.G

Blowheads wrote: »

the pipe stat for the boiler stove is set to 55-60

Even though as stated above, its very unlikely that the circ pump cuts out with the boiler, I would ensure that it isn't by the method suggested, removing the vent plug and observing the end of the pump shaft for rotation with the room stat calling for heat but the boiler off.

The run stat was replaced twice..... was the hi limit stat ever replaced or does it come as a a combined unit with the run stat?
When you removed the run stat phial was there much scale/crap in the thermo well pocket?, I'm just wondering if there was/is that it may make the stat(s) reaction time very slow with the water temperature eventually reaching the Hi limit cut out point even after the run stat has cut out the burner.

If all else fails, I would renew the hi limit stat (if not already done so) and the circ pump which probably owes you nothing anyway, a bit of expense, but as we all know nuisance/random trips are the most frustrating of all.

Wearb

If you want to check the pump and its too hot to put your hand on it, use a wooden broom handle/spoon and put one end on the pump and other pressed against your ear. You will hear it perfectly if its running.

Blowheads

Wearb wrote: »

If you want to check the pump and its too hot to put your hand on it, use a wooden broom handle/spoon and put one end on the pump and other pressed against your ear. You will hear it perfectly if its running.

Cool idea.
The boiler stat and high limit are all one unit, I'll pull it out and see can I clean inside the "hole"

I'll check ASAP the pump running with or without the boiler

jimf

both stats can be bought separate

Blowheads

The circulating pump is set to 3

The circulating pump runs for as long as the internal stat calls for heat

If boiler gets to temp and I turn down the boiler stat AND the internal stat is still looking for heat the circulating pump continues to run. So the circulating pump is driven by the internal stat

Re the probe stat, would there be any benefit of splitting them as opposed to the combination one? I'd have to get an electrician out as well, would you recommend it? And anyone know an electrician that does that near Tuam?

agusta

No point getting an electrician,its a competent boiler service technician you need.the circulation and boiler are wired correctly

Blowheads

Someone above said to install a separate boiler stat and a high limit stat compared to the unit I have which is combined

What would a competent boiler service technician do specifically?

John.G

jimf wrote: »

both stats can be bought separate

That means that there are two sensing phials in the pocket?

What does a combination unit mean, is it one sensing phial in the pocket and how does that operate two separate switches?

Blowheads

John.G wrote: »

That means that there are two sensing phials in the pocket?

What does a combination unit mean, is it one sensing phial in the pocket and how does that operate two separate switches?

This is the one I have is a dual stat and high limit cut out, see picture attached

agusta

Blowheads wrote: »

Someone above said to install a separate boiler stat and a high limit stat compared to the unit I have which is combined

What would a competent boiler service technician do specifically?

i dont think anyone said to install a separate boiler stat. A technician will check everything and test before replacement. if not it just plug and play and guesswork.To get value get the boiler serviced at the same time

John.G

Blowheads wrote: »

The circulating pump is set to 3

The circulating pump runs for as long as the internal stat calls for heat

If boiler gets to temp and I turn down the boiler stat AND the internal stat is still looking for heat the circulating pump continues to run. So the circulating pump is driven by the internal stat

Re the probe stat, would there be any benefit of splitting them as opposed to the combination one? I'd have to get an electrician out as well, would you recommend it? And anyone know an electrician that does that near Tuam?

If they were installed originally as two separate units then I wonder do Grant approve of the combination unit.