I have a gas back boiler heating system that is programmed from an acl switchmaster sm400. There is no thermostat on the hot water cylinder and this has been highlighted as a real safety issue. The programmer is difficult to access so before I try I wanted to know if it is possible to retrospectively attach a cylinder stat to this model of programmer. Thanks for any advice you can give
heating programmer
- Thread starter TREEHOUSE
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Well, as you have been told that, I presume the answer is yes.
It is just a switch.
It is just a switch.
probably better off in the plumbing forum.
Depends what the safety issue is.
If you shut the pump power down (by Tstat), then the back boiler can overheat I believe which is probably more dangerous.
Look into it before just fitting a Tstat (and possibly making it worse)
Depends what the safety issue is.
If you shut the pump power down (by Tstat), then the back boiler can overheat I believe which is probably more dangerous.
Look into it before just fitting a Tstat (and possibly making it worse)
Indeed - and it seems almost inconceivable that any programmer would not have provision for a cylinder stat.
I'm not actually sure how/why the absence of the cylinder stat should be regarded as a "real safety issue". It won't do any harm to the system, so AFAICS, the only danger is that the hot water would get hotter than one wanted - but, even with a stat, 'neat' DHW is often hot enough to do one a nasty, so I'm not too sure what is being said.
Kind Regards, John
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I am not sure I understand the reservation.
Obviously a hot water cylinder requires a thermostat if only for efficiency and economy not to mention safety.
Its operation when removing demand would be no different than that of the programmer and any provision for over-run, if required, will, if the system is correctly installed (although it would appear not), already be in place.
Obviously a hot water cylinder requires a thermostat if only for efficiency and economy not to mention safety.
Its operation when removing demand would be no different than that of the programmer and any provision for over-run, if required, will, if the system is correctly installed (although it would appear not), already be in place.
It would certainly be odd not to have a cylinder stat but I'm not convinced that it's absence would be a major issue. If one wanted to have the DHW temperature close to that of the primary (boiler) water temperature, then a stat would not make much difference to efficiency/economy - and, as I've already said, I'm not sure what the perceived safety issue is (unless just a matter of the water temp).
Quite. Operation of the stat would be no different from operation of the timer. As Andy has said, if the presence/absence of a stat made any difference at all, it would be because of other deficiencies of the system, and in that case it would be the presence (not absence) of a cylinder stat which might conceivable represent a 'danger' to the system. That's how I see it, anyway!
Kind Regards, John
What might this 'danger' be?
Afaict cylinder stats are a fairly recent thing, the system at my parents house certainly didn't have one until the boiler was replaced recently.
As I said, the presence of a cylinder stat could only present a problem if there were other things wrong with the design or functioning of the system. As Andy said, if the thermostat were to shut down a pump or close a motorised valve in a system which was flawed or faulty, it might conceivably result in a problem. Very unlikley, though.
However, I only mentioned that to contrast with the fact that I cannot see any way in which the absence of a cylinder stat could threaten the system in any way. Let's face it, traditional solid-fuel indirect water heating systems didn't have (and really couldn't have had) any thermostatic control - and, as plugwash has implied, I think you'll probably find a good few current-day systems with no cylinder stat.
Kind Regards, John
Ok, fair enough.
So you should not have a cylinder stat if your system is incorrectly installed.
Further, there are a lot of central heating systems which do not have a room thermostat.
However, they should have one.
Obviously it should be installed properly.
Perhaps it is the OP's information which is incorrect and the system is such that it does not require one.
So you should not have a cylinder stat if your system is incorrectly installed.
Further, there are a lot of central heating systems which do not have a room thermostat.
However, they should have one.
Obviously it should be installed properly.
Perhaps it is the OP's information which is incorrect and the system is such that it does not require one.
I'm not sure that "incorrectly installed" is necessarily true. I would say that you should not have a cylinder stat if your system is designed/installed in a manner that is not intended to support a cylinder stat (although I would imagine that the vast majority of installations are designed/installed in a manner which would support one).
I thought the modern idea/fashion was not to have a room stat but, instead, to have TRVs one each radiator?
As I've been saying, I'm not sure that any system actually 'requires' a cylinder stat, provided that one is happy with the DHW temperature one gets without one. I certainly don't think that any system 'requires' one for any reason other than to control the water temp.
kind Regards, John
It is, indeed and what happens when all the TRVs are closed?
The boiler cycles - all summer.
The same as when the water is hot enough without a cylinder stat.
The same as when the water is hot enough without a cylinder stat.
Sorry but I don't see where there is a safety issue if no cylinder stat is present.
A cylinder stat would set the limit for heating the DHW via a motorised valve but without the cylinder stat the gas boiler stat would control, abeit less efficiently, the temperature of the DHW.
So, as far as safety is concerned the gas boiler stat has overall control and I can't see why there is any safety debate required.
Yes, in a modern day installation a cylinder stat is obviously required, but gas back boilers go back donkey's years, when the more sophisticated control mechanisms were not commonplace and thermosyphon principles were used to heat DHW rather than the pumped methods in use today.
A cylinder stat would set the limit for heating the DHW via a motorised valve but without the cylinder stat the gas boiler stat would control, abeit less efficiently, the temperature of the DHW.
So, as far as safety is concerned the gas boiler stat has overall control and I can't see why there is any safety debate required.
Yes, in a modern day installation a cylinder stat is obviously required, but gas back boilers go back donkey's years, when the more sophisticated control mechanisms were not commonplace and thermosyphon principles were used to heat DHW rather than the pumped methods in use today.
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