the thermostat "under my heater" for the boiler has setings Lo/1-4/Hi. After the last annual service i note that i has been set to hi whereas as it used to be 2-3.
I have thermostatic valves on most radiators but i find that if the central heating is on for a while [ie allnight during the recent cold snap] and all the house is hot, even if the temp is higher than the room-thermostat-temp the boiler is still "on".
the hot water is also very hot so i dont see why that would cause the need for conitnued curning. i turned the boiler thermostat down to 2 and it stopped immediately and since then the house is as hot as it was before and the water is as hot as before so what does this boiler-thermostat setting affect? can i not just turn it down to 1 or low?[apologies for the wordy post but i couldnt explain my confusion succinctly]
the thermostat "under my heater" for the boiler has setings Lo/1-4/Hi. After the last annual service i note that i has been set to hi whereas as it used to be 2-3.
I have thermostatic valves on most radiators but i find that if the central heating is on for a while [ie allnight during the recent cold snap] and all the house is hot, even if the temp is higher than the room-thermostat-temp the boiler is still "on".
the hot water is also very hot so i dont see why that would cause the need for conitnued curning. i turned the boiler thermostat down to 2 and it stopped immediately and since then the house is as hot as it was before and the water is as hot as before so what does this boiler-thermostat setting affect? can i not just turn it down to 1 or low?[apologies for the wordy post but i couldnt explain my confusion succinctly]
Are you sure the boiler control is a thermostat? Mine goes from min - max, but there's no thermostat - if the weather gets colder, we turn it up. If the weather gets warmer and we leave it turned up, the house gets too hot. AIUI thermostats to control the boiler are normally aray from it and other sources of heat, usually on a wall in the living room or similar.
The boiler thermostat controls the temperature at which the water leaves the boiler. Unless you have a boiler interlock, the boiler will cycle on and off on its own stat, just to keep itself hot, even when no heat is required by the CH or HW - which is wasteful (and against the regs for recent installations).
What you need is a room thermostat which turns the whole lot off when the house is hot. This needs to be located in a room whose radiator *does not* have a TRV - otherwise there is a conflict.
You also need a tank stat on the hot water cylinder to indicate when the HW is hot enough - with the whole lot integrated into one of the recognised control schemes (called 'plans' by Honeywell).
Do you currently have any stats besides the one on the boiler and the TRVs on the rads? Do you have any motorised zone or diverter valves in the system? [Have a look at the plans in
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and see whether any are similar to what you have].
Was interested in the point about against current regs. Recently (Within last week) weve had a combi boiler installed in a 3 bed house all rads have TRVs but there is no room stat. Is this required by the regs then or can some boilers get away without having one?
The thermostats in the system should do the following:
The hot water cylinder thermostat should cause the boiler to fire up when the hot water gets too cold.
The room thermostat should cause the boiler to fire up when the room it is in gets too cold.
The thermostatic radiator valves should turn the individual radiator down when the room gets too hot, but won't make the boiler fire or stop at all.
The boiler thermostat sets the temperature of the water that goes through the radiators and reheats the hot water.
There appears to be something wrong with the control systems if the boiler doesn't stop firing when neither the room thermostat nor cylinder thermostat calls for heat. Either a wiring fault or a thermostat fault could cause this. Does the boiler fire even with the room thermostat and cylinder thermostat set really low?
As for setting the boiler thermostat, there's a few parameters to juggle.
Advantages of setting low: Better thermodynamic efficiency Safer radiator temperatures
Advantages of setting high: Greater radiator heat output (especially useful in cold weather) Prevents condensing operation and corrosion
the operating instructions on the back of the removable front plate on the heater [it is a back boiler] refer to it as a thermostatic knob. I do have a separate room thermostat in the hallways as well as the radiator TRVs; the hot water cylinder is in the loft and i dont know if it has a separate thermostat.
having the heating on so much is resulting in really hot water in the morning [maybe this is just subjective, however].
since i am finding the house is getting hot enough, from what has been said here am i safe to assume that i can turn the "thermostatic knob" for the boiler down to 1-2 to provide "background warm" over a longer period?
as i said, at time even when the hot water from the taps is very hot and the rooms are all hot [or if i turn the wall thermostat down to simulate this] sometimes the boiler is still firing away....
the operating instructions on the back of the removable front plate on the heater [it is a back boiler] refer to it as a thermostatic knob. I do have a separate room thermostat in the hallways as well as the radiator TRVs; the hot water cylinder is in the loft and i dont know if it has a separate thermostat.
having the heating on so much is resulting in really hot water in the morning [maybe this is just subjective, however].
since i am finding the house is getting hot enough, from what has been said here am i safe to assume that i can turn the "thermostatic knob" for the boiler down to 1-2 to provide "background warm" over a longer period?
as i said, at time even when the hot water from the taps is very hot and the rooms are all hot [or if i turn the wall thermostat down to simulate this] sometimes the boiler is still firing away....
AIUI, there *must* be a boiler interlock - which turns the boiler right off when the heating demand is satisfied. There *are* ways of doing it other than with a room stat - but a stat is by far the easiest.
Ask your plumber how he has addressed this requirement!
It is distinctly possible that you've got a gravity hot water system and pumped central heating system. Have you got 4 pipes connected to the boiler - 2 on one side going to the hot water tank in the airing cupboard, and 2 on the other side going to the radiators? [This is quite common with back boiler systems such as the Baxi Bermuda].
The problem with this sort of system is that the room stat only turns the pump on and off, and the boiler runs whenever heating is turned on at the programmer - and the hot water goes on getting hotter.
If you want to exercise some control over it, and save a lot of energy, you'll need to add some additional components. The best solution is to go fully pumped and use a couple of zone valves to convert it to an S-Plan. [See
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simpler alternative which is not quite so good, but a whole lot better than what you currently have is to put a zone valve and cylinder stat in the HW circuit, and convert it to a C-Plan. This provides the necessary boiler interlock to ensure that the boiler only fires when either or both stats are calling for heat. But the HW circulation is still gravity, so HW recovery will be slower than if it were pumped.
cheers set square you have hit lots of nails on heads. i do indeed have a baxi bermuda backboiler system. the hot water cylinder is in the loft with the cold water tank in a gravity system [hence i am having a shower pump fitted].
disappointed to note what you say [in the energy efficiency sense, not in your reply!] as i have just forked out of TRVs etc to aid efficiency/bills reduction and now it seems it wont happen unless i get my HW circuit overhalled.
i have just bought a Stuart Turner Showermate Pump which isnt suitable for a whole pumped system but within these limits then what can i get the plumber to do with the hot watr circuit at the same time as he is putting the pump in to make it more energy efficient? is it to put this zone valve malarky in the HW circuit? if so is it complicated to do - the guy is a builder by trade but certainly not a fully-fledged plumber.....
The requirement is for a boiler interlock. This means that the boiler must entirely shut down when there is no call for heat from the house or hot water system. This is possible on an all TRV system by having a flow switch that shuts down when the flow through the radiator gets below a certain level. However, I'm 95% certain that you don't have such a system, but just an ignorant installer, although I suppose there is always that 5% chance.
I think we need first to clear up a bit of confusion in order to distinguish between gravity and gravity!
Sure, you have a gravity fed secondary hot water system, whereby water from your cold header tank flows by gravity into the bottom of the hot cylinder, pushing hot water out of the top to your hot taps. But that wasn't what I meant.
You also have a 'gravity' *primary* hot water circuit (I suspect!). This is the water which flows from the boiler to the heating coil inside your hot cylinder and indirectly heats your domestic hot water without actually mixing with it. The flow is referred to as 'gravity' because it circulates by natural convection rather than using a pump. It's *this* circuit - which is completely independent of the domestic hot water pipes per se - which needs a zone valve in order to convert your system to a C-Plan and implement a boiler interlock.
It is not a difficult job *as long as* you know what you are doing. You have to insert the valve somewhere where it doesn't interfere with a clear path from the boiler to the fill & expansion tank (that's the second, very much smaller, header tank which you should have in the attic), and you have to get the electrical wiring exactly right. Unless your man is reasonable at plumbing and electrics, and has a good understanding of heating control systems, I wouldn't let him near it!
How is he proposing to install the shower pump? To do it properly, you need a dedicated hot feed from the hot cylinder - using a Surrey flange or whatever, and not shared with any hot taps - and you need a dedicated cold feed from the cold header tank which - ideally - is *lower* than the take-off point for the cold feed to the hot cylinder. That way, if you manage to empty the cold tank while showering, the hot stops before the cold, so it doesn't scald you!
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