Grant Vortex Outdoor Boiler and Frost Stat

smjm

Morning All!

If I understand things correctly, the Vortex Outdoor models have a built in frost stat which start the boiler and pump running when the temperature inside the casing reaches 5 degrees, in order to stop the boiler itself from freezing. Obviously that wouldn't be helpful if no valves were open for the water to flow, so the frost stat has to be wired (somehow) to open a valve for either the hot water or a radiator zone or, as I've read, a separate 'bypass' circuit. Is that correct?

My question then is: what form would the bypass take? Can it simply be thought of as a separate zone? Is it just a length of pipework with its own 2-port valve and, if so, are there certain requirements for the length and location of the pipework, and is there anything special about the valve?

Also, is it necessary to install a pipe stat on the return pipe to one of these boilers, to prevent it running constantly in cold conditions, or does the simple operation of the boiler raise the internal temperature of the casing sufficiently that the frost stat will turn off the boiler and pump (and also close the bypass or other valve)?

If you were installing one of these boilers from scratch, how you would go about setting things up with regard to the frost stat?

Hope that makes sense. Please excuse my layman terminology!

aujopimur

Fit an automatic bypass valve.

smjm

aujopimur wrote: »

Fit an automatic bypass valve.

Thanks --- that gives me something to read up on.

Does the bypass valve have anything to do with the frost-stat/pipe-stat interaction though, or would a pipe stat actually be required?

agusta

The original frost stat in the vortex was preset[fixed] at 4 to 5 degrees approx.afaik ,the frost stat is now pre set at 1 to 2 degrees,which to me makes more sense.

aujopimur

smjm wrote: »

Thanks --- that gives me something to read up on.

Does the bypass valve have anything to do with the frost-stat/pipe-stat interaction though, or would a pipe stat actually be required?

The frost stat will do, the auto bypass comes with instructions.

smjm

aujopimur wrote: »

The frost stat will do, the auto bypass comes with instructions.

Cheers. Still slightly muddled though after reading this on the Grant FAQ:

"We recommend that Outdoor Boilers should have a Frost Stat fitted. The Grant Vortex Module range is factory fitted with a Frost Stat set at 5ºC plus or minus 1ºC. A permanent live is required with a frost stat

For added frost protection on Grant Vortex Modules, fit a pipe thermostat on a return pipe, set at 30ºC and wired to number 5 & 6 on the control panel. This will prevent the boiler heating the house unnecessarily. A bypass must also be fitted when wired as above."

(http://grantengineering.ie/installers-information/faq-information-on-grant-boilers/#toggle-id-3)

Wish there was more information out there. Details seem to be in short supply!

Wearb

What the first part of that means (frost stat), is that (assuming everything is wired as expected) the frost stat is only protecting the boiler and not the rest of the pipework etc.. In that situation a bypass is not needed for that function.

The part about the pipe stat, is to protect the pipework from frost and in that case a bypass is needed.

smjm

Wearb wrote: »

What the first part of that means (frost stat), is that (assuming everything is wired as expected) the frost stat is only protecting the boiler and not the rest of the pipework etc.. In that situation a bypass is not needed for that function.

The part about the pipe stat, is to protect the pipework from frost and in that case a bypass is needed.

Okay, I can understand that, but .... now I'm back to my original post! :P

When the frost stat starts the boiler and the pump, (which I presume it does, but I'm open to correction), the water has to flow somewhere. I thought that was the idea of the bypass circuit, but you're saying a bypass isn't needed when only protecting the boiler? So what exactly should the frost stat do that protects the boiler? You said "assuming everything is wired as expected" -- I suppose that's the information I'm after, i.e. exactly what is expected?

aujopimur

It you fit the auto bypass after the outdoor pipework, ie where it enters the house, no MV is required.

agusta

The frost stat activates the boiler at 1 to 2 degrees.It starts the boiler and the pump.
The frost stat is fitted behind the control panel on the top of the boiler.The boiler will generate heat inside the boiler casing and the frost thermostat will sense the temperature rise and cut out the boiler.
Your correct,the water does need somewhere to circulate.
The motorised valves will be closed so the pump will be unable to circulate the water.This is bad for the pump and you will most certainly get nuisance trip outs on the hi-limit thermostat.
So an auto-bypass is required.fitted between the boiler and the motorised valves.If its fitted inside the house ,its gives the boiler and the outdoor pipework full protection

smjm

agusta wrote: »

The frost stat activates the boiler at 1 to 2 degrees.It starts the boiler and the pump.
The frost stat is fitted behind the control panel on the top of the boiler.The boiler will generate heat inside the boiler casing and the frost thermostat will sense the temperature rise and cut out the boiler.
Your correct,the water does need somewhere to circulate.
The motorised valves will be closed so the pump will be unable to circulate the water.This is bad for the pump and you will most certainly get nuisance trip outs on the hi-limit thermostat.
So an auto-bypass is required.fitted between the boiler and the motorised valves.If its fitted inside the house ,its gives the boiler and the outdoor pipework full protection

That makes sense, cheers!

One last question then. In a setup where we're just relying on the frost stat to start and stop the boiler according to the internal casing temperature, how often might a boiler switch itself on and off during a night? For instance, if the temperature reached 1 degree at midnight, causing the frost stat to kick in, and the external temperature remained constant for the next 6 or 7 hours, would the boiler be likely to run for 5 minutes every hour, or something like that? Given that the water was only circulating around the bypass, I'd expect the internal temperature of the casing to rise fairly quickly, causing the frost stat to stop the boiler after not too long a period -- but I've no idea how long it would take the temperature to drop again to the point where the frost stat started the boiler again. I'm only looking for a rough idea on this, of course.

K.Flyer

Depends on how cold it is and how long the temperature stays at that level.
So say if it was less than zero degree, then the boiler will activate until the internal of the casing is warm enough to turn off the stat, then the external cold will cool the boiler back down and repeat the process until the the external temperature rises above the frost stat set point.
An alternative, which I have seen done, is to wire the frost stat through one of the zone valves. Although this will run the boiler for a little longer, if the external temperature is very low it will introduce some heat into the house at the same time.

agusta

definitely not 5 mins every hour,The boiler itself will still be giving off heat for a long time after the first cut out.at a guess it might kick back in for a few mins a few hours later if it was a constant zero degrees outside

Wearb

agusta wrote: »

The frost stat activates the boiler at 1 to 2 degrees.It starts the boiler and the pump.
The frost stat is fitted behind the control panel on the top of the boiler.The boiler will generate heat inside the boiler casing and the frost thermostat will sense the temperature rise and cut out the boiler.
Your correct,the water does need somewhere to circulate.
The motorised valves will be closed so the pump will be unable to circulate the water.This is bad for the pump and you will most certainly get nuisance trip outs on the hi-limit thermostat.
So an auto-bypass is required.fitted between the boiler and the motorised valves.If its fitted inside the house ,its gives the boiler and the outdoor pipework full protection

It is a long time ago since i did an install of one of these, but I thought that -when wired in a particular way- that the frost stat called for boiler heat without running the pump. Am I remembering this incorrectly?

aujopimur

Wearb wrote: »

It is a long time ago since i did an install of one of these, but I thought that -when wired in a particular way- that the frost stat called for boiler heat without running the pump. Am I remembering this incorrectly?

Yes.

smjm

agusta wrote: »

definitely not 5 mins every hour,The boiler itself will still be giving off heat for a long time after the first cut out.at a guess it might kick back in for a few mins a few hours later if it was a constant zero degrees outside

Excellent. Thanks to you and everyone else for the help!

jimf

Wearb wrote: »

It is a long time ago since i did an install of one of these, but I thought that -when wired in a particular way- that the frost stat called for boiler heat without running the pump. Am I remembering this incorrectly?

if wired this way you would most likely run the risk of tripping the hl stat

Wearb

jimf wrote: »

if wired this way you would most likely run the risk of tripping the hl stat

I don't know where the idea I had came from Jim.
Though I suppose a frost stat would cut boiler out before it got hot enough to trip hi stat.

jimf

quite possible I suppose wearb

but if the run stat was set at max the static water in boiler would probably continue to rise in temp

Wearb

jimf wrote: »

quite possible I suppose wearb

but if the run stat was set at max the static water in boiler would probably continue to rise in temp

Don't think the boiler stat comes into play when fired by frost stat. Wouldn't even be a live feed to boiler stat unless there was another call for heat. It's late and perhaps I have this all ar$eways.

jimf

its me that probably has it arseways as usual

K.Flyer

Heating Fused Spur ===> Frost Stat ===> Switched Live Going to Boiler (or Brown on a zone valve).
Depending on how the system is set up, the feed from the frost stat will connect to the switched live going to the boiler, so that the boiler"s own thermostat still controls the boiler.
To connect after the boiler thermostat means you would have by-passed its main safety device.

Wearb

K.Flyer wrote: »

Heating Fused Spur ===> Frost Stat ===> Switched Live Going to Boiler (or Brown on a zone valve).
Depending on how the system is set up, the feed from the frost stat will connect to the switched live going to the boiler, so that the boiler"s own thermostat still controls the boiler.
To connect after the boiler thermostat means you would have by-passed its main safety device.

I have looked at the Vortex wiring diagram (should have done so at the beginning of the thread). I see now that frost stat is wired in series with both boiler stats. As KF said it needs to be like that for safety.

So Jim you're not the one who got it ar$seways after all.
I must have just noticed that it could be wired to work only through the frost stat way back then, not that it was done that way. Frost stat is likely to cut out boiler long before it gets hot enough for hi limit trip. Though it needs that for safety.
Thanks All.

jimf

I suppose if you actually think about it we could make scenarios why it needs to be this way

cover off boiler allowing heat to disperse to the outside thus only allowing the frost stat to kick in

Wearb

I heard you the first time Jim

jimf

Wearb wrote: »

I heard you the first time Jim

:P:P

smjm

Quick question, seeing as the thread is still running!

Would the frost stat normally be tested on boiler commissioning/servicing, and how would that be done (other than waiting for some cold weather!)

agusta

No,the frost stat on the vortex cant be adjusted,its preset at 2 degrees,plus or minus 1 degree.so it wont be checked during commisioning or servicing.

smjm

agusta wrote: »

No,the frost stat on the vortex cant be adjusted,its preset at 2 degrees,plus or minus 1 degree.so it wont be checked during commisioning or servicing.

Ok, thanks. I can see why it might be difficult; thought there might be some sort of test mode to simulate it though.

Dtp1979

No harm wiring the frost stat through a pipestat on the return set to 25/30. That way the bypass circuit doesn't need to get so hot. Frost stat does a more efficient job then

smjm

Dtp1979 wrote: »

No harm wiring the frost stat through a pipestat on the return set to 25/30. That way the bypass circuit doesn't need to get so hot. Frost stat does a more efficient job then

In layman's terms, what's the sequence of events in such a set up please?

Dtp1979

smjm wrote: »

In layman's terms, what's the sequence of events in such a set up please?

Frost stat fires boiler. When the boilers return pipe reaches 30 degrees it turns the boiler off. Without using the pipestat the boiler will fire until the pipes are 60 degrees roughly.

smjm

Dtp1979 wrote: »

Frost stat fires boiler. When the boilers return pipe reaches 30 degrees it turns the boiler off. Without using the pipestat the boiler will fire until the pipes are 60 degrees roughly.

Will the pipes reaching 30 degrees be enough to warm up the boiler sufficiently that the frost stat won't just kick in again?

Dtp1979

smjm wrote: »

Will the pipes reaching 30 degrees be enough to warm up the boiler sufficiently that the frost stat won't just kick in again?

The warmth of the boiler doesn't decavtivate the frost stat in the first place. Well maybe a little

smjm

Dtp1979 wrote: »

The warmth of the boiler doesn't decavtivate the frost stat in the first place. Well maybe a little

Oh! Slightly confused again then! :P

I thought the idea was that the frost stat started the boiler; the boiler running raised the temperature inside the boiler casing; the frost stat noted the increased temperature and switched off the boiler? (In a case without a pipe stat that is.)

Dtp1979

smjm wrote: »

Oh! Slightly confused again then! :P

I thought the idea was that the frost stat started the boiler; the boiler running raised the temperature inside the boiler casing; the frost stat noted the increased temperature and switched off the boiler? (In a case without a pipe stat that is.)

Kind of. But the boiler is so well insulated that it gives off very little heat. Some residual heat will help no doubt but the main reason is that the water temp will rise and the Boiler won't freeze and burst

smjm

Dtp1979 wrote: »

Kind of. But the boiler is so well insulated that it gives off very little heat. Some residual heat will help no doubt but the main reason is that the water temp will rise and the Boiler won't freeze and burst

Ok, thanks!

smjm

Another question if I may!

Does the test switch run the pump as well as the boiler/burner? If so, presuming an 'S' plan setup, would this be functionally equivalent to the frost stat kicking in, as far as testing the bypass pipework and auto-bypass valve were concerned?

Dtp1979

smjm wrote: »

Another question if I may!

Does the test switch run the pump as well as the boiler/burner? If so, presuming an 'S' plan setup, would this be functionally equivalent to the frost stat kicking in, as far as testing the bypass pipework and auto-bypass valve were concerned?

Pretty much, yes

smjm

Dtp1979 wrote: »

Pretty much, yes

Cheers!

Would it be normal to have a bypass on a 'Y' plan as well, even though there would always be a path -- presumably, normally to the cylinder -- for the water to flow if the frost stat kicks in. I was just wondering if there might be a conflict between the frost stat switching the boiler on and a cylinder stat being satisfied and trying to turn the boiler off, if that makes sense? Or would the cylinder stat not come into play if it wasn't responsible for switching the boiler on in the first place?

Dtp1979

smjm wrote: »

Cheers!

Would it be normal to have a bypass on a 'Y' plan as well, even though there would always be a path -- presumably, normally to the cylinder -- for the water to flow if the frost stat kicks in. I was just wondering if there might be a conflict between the frost stat switching the boiler on and a cylinder stat being satisfied and trying to turn the boiler off, if that makes sense? Or would the cylinder stat not come into play if it wasn't responsible for switching the boiler on in the first place?

Being honest, I never use y plan so I know feck all about it

K.Flyer

You would wire in the switched live from the frost stat to the controls switched live after the stat.

smjm

K.Flyer wrote: »

You would wire in the switched live from the stat to the controls switched live after the stat.

Thanks K.Flyer, but, as a layman, you've gone into a bit too much technical detail for me! :P

I'll write my question a bit differently, if I may. All of this is hypothetical -- just trying to get a few things straight in my head!

I've worked out that a Y plan doesn't need an ABV, (although it would benefit from having one fitted -- even if only as a backup should the 3 port valve fail.) So, in a Y plan set-up, a frost stat would generally have no need of a bypass even if it was present. That's grand.

I'm guessing that on a Y plan involving the vortex outdoor boiler, with its integral frost stat, it would make sense to wire in a pipe stat to switch the boiler off when the return pipe gets to a certain temperature -- just the same as with an S plan. Grand again!

Given the following scenario though:
- grant vortex outdoor boiler with integral frost stat
- no pipe stat on return
- (doesn't matter whether a bypass is in place or not?)
- no heat being called for, either from heating or DHW
- 3-port valve open to DHW cylinder position as default
- outdoor temp drops and frost stat kicks in the boiler and pump

would the cylinder stat be active, for want of a better word, or would the boiler, controlled by the frost stat, just keep pumping water around the DHW circuit as though the cylinder stat didn't exist?

smjm

smjm wrote: »

Given the following scenario though:
- grant vortex outdoor boiler with integral frost stat
- no pipe stat on return
- (doesn't matter whether a bypass is in place or not?)
- no heat being called for, either from heating or DHW
- 3-port valve open to DHW cylinder position as default
- outdoor temp drops and frost stat kicks in the boiler and pump

would the cylinder stat be active, for want of a better word, or would the boiler, controlled by the frost stat, just keep pumping water around the DHW circuit as though the cylinder stat didn't exist?

Going to answer my own question, as far as I understand!

The cylinder stat would be inactive, as it wasn't calling for heat in the first place, and would thus have no interaction or conflict with the frost stat, which, of course, makes sense.

Simple conclusion to all my questions: if you've got an outdoor Grant Vortex, install an ABV and a pipe stat regardless of whether you've got a Y- or S-plan set-up!

K.Flyer

Sorry, meant to reply.
Yes, effectively you are going to by-pass any room or cylinder stat, thus sending power directly to the boiler.
An ABV would be advisable, with the option of the pipe stat, but probably not really necessary.

smjm

K.Flyer wrote: »

Sorry, meant to reply.
Yes, effectively you are going to by-pass any room or cylinder stat, thus sending power directly to the boiler.
An ABV would be advisable, with the option of the pipe stat, but probably not really necessary.

Thanks K.Flyer.

As an aside, shouldn't boilers that have integral frost stats also have something functionally equivalent to an integral pipe stat, so that the two work in tandem? Not sure if any existing boilers provide such, but it would seem to be a good idea!

agusta

smjm wrote: »

Thanks K.Flyer.

As an aside, shouldn't boilers that have integral frost stats also have something functionally equivalent to an integral pipe stat, so that the two work in tandem? Not sure if any existing boilers provide such, but it would seem to be a good idea!

The frost stat does protect the boiler fully without the pipe stat.the abv is a standard in plumbing,it should be fitted

smjm

agusta wrote: »

The frost stat does protect the boiler fully without the pipe stat.the abv is a standard in plumbing,it should be fitted

Thanks agusta. If there isn't a pipe stat though, wouldn't the frost stat keep the boiler running for as long as the internal boiler casing temperature didn't rise though -- which seems wasteful? I understand that the pipe stat isn't technically necessary, but wouldn't it seem to be a good idea to have one in all cases, or are there any scenarios where a pipe stat shouldn't be fitted as the norm?

Edit: Sorry for dragging this thread on and on. I think my confusion is that I've seen what appear, to me, to be conflicting opinions about whether the frost stat's turning on the boiler is enough to raise the temperature inside the boiler casing, such that the frost stat will be satisfied and turn the boiler off again.

K.Flyer

Depending on the size of the central heating system, size of circulation pump, flow rates etc, I would think it is quite possible that the boiler casing could heat up by 2 to 5 degrees, enough to turn off the frost stat long before any pipe stat would reach temperature, unless it to is set very low.

smjm

K.Flyer wrote: »

Depending on the size of the central heating system, size of circulation pump, flow rates etc, I would think it is quite possible that the boiler casing could heat up by 2 to 5 degrees, enough to turn off the frost stat long before any pipe stat would reach temperature, unless it to is set very low.

Thanks for that. I was speaking to a plumber today who said he didn't bother to fit a pipe stat because running the boiler would easily raise the internal boiler casing temperature above the frost stat's limit, thus switching it off. He reckoned that the internal casing temperature would reach 20-25 degrees when running normally, but I guess it depends on the temperature outside of the boiler casing. I'd be surprised if it reached those temperatures if the outside temperature was zero degrees or less, but I'm not a plumber, so what do I know! :P

Robbie.G

smjm wrote: »

Thanks agusta. If there isn't a pipe stat though, wouldn't the frost stat keep the boiler running for as long as the internal boiler casing temperature didn't rise though -- which seems wasteful? I understand that the pipe stat isn't technically necessary, but wouldn't it seem to be a good idea to have one in all cases, or are there any scenarios where a pipe stat shouldn't be fitted as the norm?

Edit: Sorry for dragging this thread on and on. I think my confusion is that I've seen what appear, to me, to be conflicting opinions about whether the frost stat's turning on the boiler is enough to raise the temperature inside the boiler casing, such that the frost stat will be satisfied and turn the boiler off again.

The frost stat calls the boiler the boiler runs and heat builds up to temp and cuts out on stat because in most cases with an abv the circuit will be quite small there will be little to no circulation so the boiler won't perticularly cool and maintain heat within boiler protecting from frost damage
Yes a pipe stat could be wired in to cut out when set temp is reached but it really isn't going to make much difference unless it's a large circuit with the abv fitted a good distance from the boiler