Heatslave 25/32 CH too hot

[carl0s]

Just moved in.

Have a Heatslave 25/32.

Even with the CH temperature dial on the boiler set all the way down, the radiators are just too hot. I have had to turn down a lot of the TRVs on the rads, and even then the house just gets sweltering. This is a detached cottage on a hill and to be honest this is the opposite of what I was expecting.. I thought it might be too cold! I'm just concerned that we are not being efficient with our oil usage and I'd like to start by having the CH just as warm as it needs to be.

Any ideas?

 

[muggles]

Possibly a broken boiler thermostat, or if it's a combi the diverter might be passing. Do your radiators get hot even with the heating turned off?

 

[carl0s]

Possibly a broken boiler thermostat, or if it's a combi the diverter might be passing. Do your radiators get hot even with the heating turned off?

I'm not sure on the diverter. I will check. I have some experience of broken diverter valves, from the Vokera Linea 24 at my old house. This does seem like the thermostat or thermistor (whatever the boiler has) problem, or possibly some kind of burner calibration thing maybe? It was recently serviced or repaired, less than a month before we bought the house. The service history makes me think these things are less reliable than my 20yr old Vokera was. I could fix that myself too.

The heatslave is an oil fired combi. It has an inbuilt storage tank for the HW side so that you get quicker and hotter instant hot water, but even if the HW has been turned off, you still get instant-ish hot water, it's just not super hot, and not super instant. Good enough for a shower though.

How would a dodgy diverter valve cause the radiators to be too hot, unless we were running the taps or filling a bath or something? That's not the case here. The temperature just can't be turned down enough from the boiler.

 

[muggles]

The built in storage tank doesn't store the water that comes out of your taps, it's part of the heating circuit and is kept hot to be pumped through your plate heat exchanger to quickly heat the water that does come out of your taps. If your diverter is passing, the boiler could be sending water round your radiators whilst trying to heat up the heat store.

I'll ask again - do your radiators get hot with your heating turned off?

 

[carl0s]

The built in storage tank doesn't store the water that comes out of your taps, it's part of the heating circuit and is kept hot to be pumped through your plate heat exchanger to quickly heat the water that does come out of your taps. If your diverter is passing, the boiler could be sending water round your radiators whilst trying to heat up the heat store.

I'll ask again - do your radiators get hot with your heating turned off?

Thanks for the proper explanation of the storage tank.
I couldn't do the DV/radiator check last night because we had the CH on already.
I have checked this morning, and no, the radiators don't get hot or warm up with the CH off. This is with the HW set to 'on' all night (which I believe means it is keeping the heat store up to temp), and then having a ten minute shower in the morning, and then running the hot tap for 2 minutes. Radiators are still cold.

Another slight curiosity I have is that the shower gets quite warm, while the kitchen tap runs really hot. Do some of these boilers have an alternate-temperature output for shower use? That is something I always thought would be useful to save money - rather than heating up and then mixing with cold at the shower, but on this occasion I did want the shower just a bit hotter.

 

[jackthom]

I understand there seems to be a problem with the water temperature but you haven’t mentioned a room thermostat in all of this, which is really what you should be turning down if the whole house is getting too hot. Is it that the radiators are so hot that the house temperature is still overshooting even after the heating has turned off?

 

[carl0s]

I understand there seems to be a problem with the water temperature but you haven’t mentioned a room thermostat in all of this, which is really what you should be turning down if the whole house is getting too hot. Is it that the radiators are so hot that the house temperature is still overshooting even after the heating has turned off?

Hi. There is a room stat but it's near the front door in what I would say might be the coldest part of the house. It does work and does do its job. I'm not sure if it being in the hallway close to the front door is a good or bad thing though. It's just that I thought I should be able to control the CH water temperature

 

[jackthom]

You should be able to get the flow temperature down to around 50C which shouldn’t feel scalding hot at the radiators.
When you turn the temperature dial does the display above (if there is a display) show the set temperature and what does the display read while the boiler is running and the radiators are hot?

 

[carl0s]

You should be able to get the flow temperature down to around 50C which shouldn’t feel scalding hot at the radiators.
When you turn the temperature dial does the display above (if there is a display) show the set temperature and what does the display read while the boiler is running and the radiators are hot?

Good question. It doesn't actually tell me. I remember my Vokera did have a readout, but this one doesn't.
When we have done some more unboxing and I have found my thermometer, I'll check the temperature.

FYI here is the front panel, and also some numbers and info from a recent service / repair. (all those parts replaced on a 'general service'.. sheesh).

 

[oilhead]

If that was done on a fixed charge Worcester service, then you're a winner. If you select just hot water, do the rads heat up? If not, suspect the CH temp sensor. It may be worth taking out the sensor from the pocket and giving it a clean.