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Original poster

Can someone help with a combi boiler mystery?

7 replies

StrawberryCheese · 09/03/2015 11:05

We have an Ideal logic combi 35 boiler and in the last week or so we have noticed that the radiators will be warm even though the heating isn't switched on Confused

The boiler isn't fired up when this happens, it's status remains at 0 and our Drayton timer switch is set to off. The thermostat is set to the lowest possible 10 degrees. We have even moved the dial on the boiler so it is only in hot water mode instead of hot water and heating, but the radiators still become warm, if only for a few minutes.

I've looked at the user guide but there is only troubleshooting info if you can't get any hot water/heating. We seem to have the opposite problem. The boiler is due for a service but I wondered if there were any experts on here that could shed some light?

OP posts:
LizzieMint · 09/03/2015 11:47

Oh that's so weird! I clicked on this thread because we have our own boiler mystery and yes, it's the exact same thing. Last week I noticed that the radiator in the lounge was red -hot, despite the heating having been off for about 4 hours at that point, and the boiler not being switched on.
I turned everything off completely in order to get it to cool again and it hasn't done it since during the day but my DH noticed the radiators were hot one night at about 4am when he was up with one of the kids.
How bizarre is that? I don't understand where the heat's coming from when the boiler is off but I'm so glad we're not the only ones!

Original poster
StrawberryCheese · 09/03/2015 12:19

How surreal that you're experiencing the same thing! Fortunately our radiators don't seem to be piping hot but I suspect that's because we have the thermostat turned right down. Hopefully someone will come along and help us both out Smile

OP posts:
LizzieMint · 09/03/2015 12:21

Our thermostat was set to about 17 at the time, although the radiator was turned up to full. It's very very weird, as the boiler's not on at the time, we must have discovered miraculous energy-free heat!

PigletJohn · 09/03/2015 15:31

If you have a combi boiler and some of the radiators get warm when you run the hot taps, it is probably the diverter valve in the boiler.

If you have a hot-water cylinder it is probably the 3-port valve, which, not being a part inside the boiler. might be cheaper.

Original poster
StrawberryCheese · 09/03/2015 16:00

Thanks for the reply PigletJohn Smile I'm not certain that's how it happens every time but it's what happened this morning, I ran a bath and the radiators got warm despite the boiler only being in hot water mode. Our boiler is still under warranty as its a new build flat so I shall give them a call.

OP posts:
LizzieMint · 09/03/2015 21:59

PigletJohn, in our case it must have been the hot water tank I would think, the tank was very hot.
I'm still slightly baffled as to why it was so hot, several hours after the heating and hot water switched off? I touched the pipe coming out of the tank to check the temp and I couldn't keep my hand on it.

PigletJohn · 09/03/2015 22:11

it might be that the ball in the 3-port valve is worn out and is permitting hot water from the boiler to flow even when the valve should be shut. The valve includes a switch which can turn the boiler off when shut. It could also be an electrical fault or the cylinder stat might have been turned too high or come unstrapped from the cylinder. 3-port is I think more likely as they do wear out after 20 years or so.

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