Frost stat with low temp Pipe Stat - But radiators heat up

[solorize]

Hi, wonder if someone can advise with the below.

I have a Worcester Bosch Greenstar 18Ri regular boiler within my garage
which has a separate, Honeywell T4360 Frost Thermostat on the wall.
Also installed to the boiler Return pipe is a Honeywell Low Limit PipeStat_L641B1004.

Stats are set as below:
Frost Stat is set at: 5°C
Low Limit Pipe Stat is set at: 15°C

I have also looked at my boiler information and its states;

We recommend that the Frost
Thermostat is installed at the
coldest location. Frost
Thermostat to be set on at 5°C
and the Pipe Thermostat to be off
at 15°C.

Which ties in with my current settings above.


Now the weather has turned cold, the frost protection has been activating, as the
temperature in the garage is below 5°C, and the boiler and Central Heating pump have
been coming on. Then when the temperature on the Return pipe reaches 15°C,
it turns the boiler back off. Which I have observed while in the garage and seems
to be happening quite frequently. Which I guess is ramping up my Gas usage
(Not sure how much this will be costing having this happen so often, especially with
the way current energy prices are).

So, onto my actual question: While the Frost protection is activating
should my radiators be heating up? As they seem to be constantly warm/hot,
which is most of the day and night while the temperature is low.

NOTE.
Even if I turn my 'house thermostat' to say 12°C (so I know there is it is
not calling to fire the boiler up), the radiators still heat up from when
the frost stat protection kicks in and fires up the boiler. hence my query above.

With the above in mind, is the following a correct assumption?
When the frost stat kicks in and fires up the boiler, this then heat the water and will
then send that heated water around all the whole central heating system / radiators,
to finally come back to the boiler via the Return Pipe, which the temperature of is then
sensed by the Low Limit Pipe Stat, which then when it reaches 15°C, will then turn the boiler off.

Which I guess would be why the radiators are heating up?

Also, to prevent the frost protection constantly kicking in, could I lower
the temperature at which the Low limit pipe stat turns the boiler off,
from the current 15°C, to a lower value to stop the radiators heating up as much
or would this be detrimental to the whole frost protection system.

Thanks in advance.

[Deleted-user-3]

from what i can tell, the system is doin exactly what its supposed to do i.e. stopping your pipes freezing up (including the boiler) thereby saving a catastrophic burst pipe scenario.. Yes if the boiler lights, and the pump runs, its going to circulate the circuit wherever that may go. i.e. into the house rads.
i kind of get where youre at though... the boilers in the garage where its freezing cold because its not insulated so the temp drops quite rapidly but the house doesnt drop so rapidly so youd rather not spend the fuel heating it when you dont need to...
maybe you could install a bypass system similar to the one in the boiler but manually or electrically operated so the flow side never leaves the garage and gets diverted straight back to the return side before it gets into the house but comes in the return before it gets back to the low limit stat..
so say in simple terms you install a "t" off the flow that goes to a valve (electrical like a 2 port zone valve or an inline lockshield) and from that t's into the return, before it gets out the garage...
when you want no or very little heat in the rads and just want the frost protection system to protect the boiler and garage pipework you just open this valve, the heated water will circulate back towards the low limit stat very quickly thereby turning the boiler off much quicker.
It doesnt protect the house pipework however so should the house drop below freezing expect a catastophe..

Failing that, if youre not using the house, drain it down and turn it off?

[solorize]

Hi cwplastering,

Thanks for you reply.

I think I would rather leave the pipework as is, just so I don't complicate matters.

I managed to find my boiler installation manual, which states that the
boiler has its own internal frost protection:

Frost protection snippet from boiler installation manual:

Automatic Internal Frost Protection.jpg (46.08 KiB) Viewed 1803 times

So now I am wondering if the separate ‘frost stat’ and ‘low limit pipe stats’ are actually necessary?
And if I can just use the boilers inbuilt frost protect only?

If that is the case, would the inbuilt frost protection be enough to protect the boiler/pipes
within the garage, and therefore I could get both the additional frost and pipe stats disconnected.

Also, would the boilers internal frost protection prevent the radiators heating up when it activates?

If it is advisable to keep both the separate stats connected;

Could I try and reduce the 'pipe stat' temperature from 15°C to say 10°C to try and
reduce the frequency of the boiler firing for frost protection, or would this be detrimental
to protecting the boiler.

[Deleted-user-3]

im not sure m understanding your apparent need to keep the radiators stone cold?
if the boiler lights it will start the pump and heat the water. If the pump starts it will circulate the water throughout the system. The "system" includes whichever radiators have open valves. If you turn off the valves they wont get warm. The heated water will return to the boiler not much cooler than when it left.
The frost protection in the boiler is designed to stop water in the system from freezing, expanding and possibly breaking the "system"
Why you have fitted or someone else has fitted a secondary frost protection system is beyond me if the boiler has its own frost protection? Have you contacted the installer?
You can see from the above flowchart exactly what happens during a frost protection cycle, you seem to have 2 systems doing a very similar thing only your external version waits until the return temp is 15 degrees as opposed to 12 degrees.
As you say this happens

As they seem to be constantly warm/hot,
which is most of the day and night while the temperature is low.

then I must assume you are not using the system to heat your home, or your home is empty, or you simply do not want the system to work as it should in cold weather then why dont you just drain the system and switch it off where it will be perfectly safe until you do wish to use the system?
This extra protection that is added, I have no information as to when i.e. before or after the boiler installation, either way it would appear to be surplus to requirements on the condition that the temperature at the boiler is not significantly higher than the temperature at the external frost stat as measured at the pipe. I also have to assume the pipework is correctly insulated where it is exposed to cold.

If your radiators are getting hot and your room thermostat is NOT calling for heat then something is broken as either one of your frost protection systems does not heat the water flowing though the radiators above 15 degrees c which you wouldnt notice as "hot". the internal built in system will only reach 12 degrees.

you could try disconnecting the external frost stat from the electrical supply and check to see if the boiler does actually light when its cold (as it should) but only until it satisfies its own condition (which is 12 degrees return, hardly "hot")
your external frost stat could be at fault so this will prove whether it is, if the boiler lights, pump runs, up to temp? boiler goes out, pump circulates water for a few minutes to dissipate and even out heat (pump over run), every thing shuts down again then your boiler is working fine and either the temp at the frost stat sensors (both flow and return) is significantly different to the temp in the actual boiler or its broken. kaput.

[ericmark]

Normally we have TRV's on the radiators, so even if the heating in general is on, the radiator should not get warm unless set to come on. I have set mine like this,

51RAAw1+hEL.jpg (64.06 KiB) Viewed 1743 times

but if using mechanical heads you will not have a time option, I used eQ-3 heads which cost me £15 each in 2019 when I fitted them.

More complex systems the TRV heads link to the thermostat/hub, but they cost more like £50 each, so gets a bit expensive, there is also the Terrier i30 which is not linked, but the 20th century mechanical type don't have the ability to set a time.