Central heating - thermostat & possibly receiver not working

[starfish4]

We have a Worcester Bosch boiler. It won't come on unless it's set on a minimum of 20c and even so has only come on a couple of times while set on timed. If it doesn't come on, we just turn the dial up a degree or two and the boiler heats the house until say 22c is reached. If it's on timed and has come up to temperature, it doesn't come on again in that time period unless you turn dial up, even though temperature has dropped. If you turn the thermostat dial it clicks twice around 19c and 22c. You can hear the mechanical timer on the boiler click at the time it should come on.

Does anyone have any thoughts? If it's just the thermostat, can heating plumber deal with this as I suspect it's wired into the electrics, ie not wireless.

Do you mean the thermostat on the boiler, or the thermostat on the wall?

The thermostat on the wall.

I have the same problem. My wireless wall thermostat has to be in the same room as the boiler and be set at 24c before it works. Even then it can't be relied upon.

Satinlaces, I think our thermostat is wired into the electrics. I don't like it too hot, so at the moment I'm really hot or really cold.

you say it has a dial, so I expect it looks like this

They have a bit of slack between the on and off positions (digital stats are more precise*). So if you set it to 20C, it will maintain a temperature between about 19C and 21C, or possibly between 18C and 22C. Depending on the size of your radiators and how well insulated and draughtproofed your home, it may take half an hour or so for the temperature of the rooms to settle down. The more often you fiddle with the stat, the more often you will feel too hot or too cold.

If it is close to a radiator, then the warm air from the rad will heat it more quickly, and it will turn the heating off until the radiator has cooled down. This is undesirable.

Larger radiators, and a boiler set to a lower running temperature, tend to maintain a more even room temperature.

TRVs can be fitted to radiators to prevent individual rooms getting hotter than you want. The radiator in the room with the wall stat should not have a TRV, and should be adjusted to warm up slower than all the others, or the others will never get warm enough.

I am not very keen on wireless stats as they have extra potential points of failure. They are however quite quick to install as they do not need wiring to the wall.

*if you decide to change to a digital wall stat, get a Honeywell CM907. It will almost certainly connect straight onto the wires from your old stat with no other changes needed, and it has numerous other advantages as it is programmable. The cables to a wall stat carry mains voltage so power must be turned off before starting work.

Thanks, PigletJohn. Yes, it does look something like the Honeywell thermostat.

The radiator is a good sized one, but on a different wall. The heating dial is set at 4 on the boiler as we found house was getting too warm too quickly for us, especially as it has to be set higher than we'd like. I think I'll turn our living room TRV down a little in the meantime then.

Do you think a heating engineer/plumber (not sure of his correct title), could change this for us, given it's wired into the electrics? That way, he can check it's functioning correctly with the boiler.

heating engineer can easily change it, so could most electricians.

If you have any doubt that the boiler is reacting correctly to the stat, get a heating person.

If you get a CM907, you can set different temperatures for different times of day and days of week - e.g. 6.30-7.30 20C, 7.30-16:00 12C, 16:00-23:00 22C, 23:00-06:30 15C. But weekends 7:30-16:00 20C; 16:00-23:30 22C; and different settings for Wednesdays; or whatever suits you. It also has overrides, late extension, and holiday settings which protects against frost for X days, then put the heat on the day you're due back.

Thank you. The boiler has a mechanical timer on it, so makes sense to contact a heating engineer who would know if a CM907 is suitable for the system. Sounds like a good idea, as we get up later at weekends, so don't necessarily want the heating on so early. Also, he will know if system is working as it should following installation.

Thanks for posting this OP- we have an almost identical problem, and I had no idea I could possibly get a replacement thermostat. We can set a timer directly on the boiler, but that doesn't help us keep the temperature constant at home, so we're also either too cold or too hot and I'm always fiddling with the thermostat.

when you fit a CM907, it takes over the timing program for the heating, and you set the boiler timer to "On". The CM907 prevents it heating up outside your programmed times.

And OP, I hope you don't mind me hijacking your thread slightly, but if I could just ask PigletJohn while he's on this thread - is it better to set a thermostat as you mentioned above at a lower temperature when you're out at work etc. or to set the boiler timer to 'off' when you're out.

in mild weather like this, if you just have a simple timer and a simple stat, set heating "off" before you go out, to come back on half an hour before you expect to return.

There are some people who think it is more economical to heat the house 24 hours a day, but they are wrong.

If you think you will be comfortable at 15C or some lower temperature, still turn the heating off before you go out, and let the timer turn it back on so it is up to 15C by the time you come home. In England, there is often enough solar gain through the windows that very little extra heat is needed most days to heat to 15C.

Insurers usually say that a house which is unoccupied during winter should be heated to 12C unless all the water has been turned off and drained out.

Thanks PigletJohn, that's really useful. We're in Scotland, so not quite so mild most of the time, but that makes sense and that's what we've mostly been doing anyway. Our thermostat is wired in, so I'll definitely look into replacing it with a digital one at some point so we don't have to fiddle about with it when the heating's on and we're at home. Many thanks!