How does boiler interlock work?
- Thread starter DIYknot
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Ok having just given a recent brief to fellow engineers on this matter, I might be able to help explain not only what an interlock is, but how to answer your question (I said might)
An interlock is by definition either, 'safety' or 'efficiency'
A safety interlock can be an air pressure switch, an over heat thermostat or anything that prevents an appliance from firing up if it would result in the appliance nor being safe. A flow switch within the boiler on the primary circuit would be a safety interlock as would a low water pressure cut off device, both of which would prevent the appliance from firing if no water is present, or pump failure/blockage.
There are of course several other types of safety interlock.
An efficiency interlock is a device that prevents the appliance from firing up for reasons of efficiency. This can be a time clock, or devices such as a room thermostat.
A zone valve could be described as both, it shuts off the boiler in conjunction with the room/cylinder thermostat, or if fitted on an unvented cylinder with a mid position valve the E.C.O. valve acts as a secondary safety device preventing flow to the cylinder if the overheat stat goes closed circuit, but we digress.
So now lets get back to the original question.
Option 1:
yes, this is quite possible and is how I run the heating in my house. I have my room stat set to 24*c in the evening but the only rads that will ever get this high are the front room rads on maximum (about 30*c I believe) and my hall rad which is my control/bypass rad. More on this rad later. The other radiators throughout the house are set from any where between 10* - 20*c so that each room reaches temperature they shut down rather than heating rooms that I don't require heating to full capacity.
Option 2:
Yes, this too is possible. I could set my TRVS to 25*c and leave my room thermostat at 18*c. However as a heating engineer, why ?
It demonstrates a lack of understanding of the system and the majority of my late night call outs relate to this question.
Option 3:
Now we are getting somewhere. This is how a heating system should be installed. Where ever the room thermostat is located the radiator in that location should not have a TRV on it, this is to allow it to act as a control radiator for the room thermostat, else wise if you turn that TRV too low the room stat will never achieve temperature and the boiler will never turn off until the end of its timed demand.
The radiator in this location should be sized accordingly (never is though is it, let's be honest neither is mine) if it is too small it will never achieve set point temperature if it is too large it will achieve it too soon.
The point you make at the end of option 3 is extremely valid and basically true, but here's the ring dinger. Central heating is an art, not rocket science. I could almost achieve what you are asking, the cost of setting it all up correctly and the time involved far out ways the benefit.
Just like I could achieve the stated miles per galleon car manufactures claim, but to do so would mean lowering car tyre pressure, never travelling up a hill and many other factors that I can't be bothered with when taxiing the kids around.
Like far greater minds than mine have said, it's a bit of a compromise.
Does this explain it any better? Or am I just rambling after a 70hr week.
An interlock is by definition either, 'safety' or 'efficiency'
A safety interlock can be an air pressure switch, an over heat thermostat or anything that prevents an appliance from firing up if it would result in the appliance nor being safe. A flow switch within the boiler on the primary circuit would be a safety interlock as would a low water pressure cut off device, both of which would prevent the appliance from firing if no water is present, or pump failure/blockage.
There are of course several other types of safety interlock.
An efficiency interlock is a device that prevents the appliance from firing up for reasons of efficiency. This can be a time clock, or devices such as a room thermostat.
A zone valve could be described as both, it shuts off the boiler in conjunction with the room/cylinder thermostat, or if fitted on an unvented cylinder with a mid position valve the E.C.O. valve acts as a secondary safety device preventing flow to the cylinder if the overheat stat goes closed circuit, but we digress.
So now lets get back to the original question.
Option 1:
yes, this is quite possible and is how I run the heating in my house. I have my room stat set to 24*c in the evening but the only rads that will ever get this high are the front room rads on maximum (about 30*c I believe) and my hall rad which is my control/bypass rad. More on this rad later. The other radiators throughout the house are set from any where between 10* - 20*c so that each room reaches temperature they shut down rather than heating rooms that I don't require heating to full capacity.
Option 2:
Yes, this too is possible. I could set my TRVS to 25*c and leave my room thermostat at 18*c. However as a heating engineer, why ?
It demonstrates a lack of understanding of the system and the majority of my late night call outs relate to this question.
Option 3:
Now we are getting somewhere. This is how a heating system should be installed. Where ever the room thermostat is located the radiator in that location should not have a TRV on it, this is to allow it to act as a control radiator for the room thermostat, else wise if you turn that TRV too low the room stat will never achieve temperature and the boiler will never turn off until the end of its timed demand.
The radiator in this location should be sized accordingly (never is though is it, let's be honest neither is mine) if it is too small it will never achieve set point temperature if it is too large it will achieve it too soon.
The point you make at the end of option 3 is extremely valid and basically true, but here's the ring dinger. Central heating is an art, not rocket science. I could almost achieve what you are asking, the cost of setting it all up correctly and the time involved far out ways the benefit.
Just like I could achieve the stated miles per galleon car manufactures claim, but to do so would mean lowering car tyre pressure, never travelling up a hill and many other factors that I can't be bothered with when taxiing the kids around.
Like far greater minds than mine have said, it's a bit of a compromise.
Does this explain it any better? Or am I just rambling after a 70hr week.
Flocking 'ell, another Which? Magazine drone.
Get a proper professional that understands controls.
Which? Should be printed on absorbant paper, then it would at least have a purpose.
Get a proper professional that understands controls.
Which? Should be printed on absorbant paper, then it would at least have a purpose.
As DIA has stated, a correctly sized system will calculate the Heatloss for each room, so if the heating system is on, the Livingroom radiator will maintain an ambient temperature of 22*C & 16-18*C in the Hall - where the room thermostat should be sited.
Since the introduction of condensing boilers, requiring a lower mean water temperature for optimum running costs, the temptation is to double up radiators in greatly improved insulated new homes. Also, many Builders have radiator manufacturers carry out Heatloss calcs, who'll oversize for commercial reasons.
Since the introduction of condensing boilers, requiring a lower mean water temperature for optimum running costs, the temptation is to double up radiators in greatly improved insulated new homes. Also, many Builders have radiator manufacturers carry out Heatloss calcs, who'll oversize for commercial reasons.
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If you find the boiler is staying on for a long time to satisfy the hall thermostat after the TRVs have been satisfied then you turn the hall thermostat down till you find the point where it stays on long enough to satisfy all TRVs and shortly after the interlock will kick in. I don't really see what all the fuss is about. Surely the TRVs will operate themselves and only once the hallway has reached temperature will the boiler shut down. It's done this way as the hall way takes longer to heat. This ensures all other rooms can reach temperature before the interlock shuts it down. It doesn't require much gas to heat the small volume of water that is within the hallway radiator and the pipes feeding it.
Thank you for taking the time to give a very well considered answer to my question. Just the sort of thing I was hoping for.
Unfortunately I was aware when asking it that I risked getting some abusive or knee jerk reactions from those who just carry on doing what they've been taught or what they've been doing for years without having the interest or intellect to ever question 'why'?
A 'proper professional' should be qualified enough to understand the physics of what they do , be willing to explain it to support their view and question it when necessary. They would not simply be abusive and dismiss the Consumer Council's analysis of several hundred customer's views on the reliability of different boiler manufacturers. (And how do you know I'm not a 'proper professional'? Who do you think assesses fitters when they apply for Gas Safe registration?)
Are you telling us you are not industry professional who doesn't understand interlocks? . What is dry cycling?
I assure you that I am quite capable of independent thought free from outdated regulations.
Also, I was not being abusive to you personally, merely the publication.
The pointlessness of Which? Magazine has been discussed her several times recently and, in the case of boilers, soundly proved to be in desperate need of absorbative properties.
I assure you that I am quite capable of independent thought free from outdated regulations.
Also, I was not being abusive to you personally, merely the publication.
The pointlessness of Which? Magazine has been discussed her several times recently and, in the case of boilers, soundly proved to be in desperate need of absorbative properties.
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