Why does Combi boiler delay heat delivery to radiators but not to hot water taps?

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Hi

I have a Grant Vortex Pro 36 Electronic Condensing Combi Oil Boiler
(PDF Manual is here).

For the taps the hot water delivery is immediate and as soon as the hot water tap comes on. It's hot as soon as the length of pipe is flushed out.

Radiators are sometimes almost instantly hot, as soon as the heating switch goes on, though sometimes it can take half an hour for the radiators to warm up; then they get as hot as they should.
(hot water tap is off and so is combi fed shower when this is happening. Nothing else is drawing water from the combi boiler when this is happening.)

Anyone any idea what is going on?

(there is a red pressure vessel/ bladder inside, I remember this was replaced in the past, could this be the problem?)
 
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Your boiler will always give priority to hot water. If the boiler is cold, then when switched on, you will get no heating until the heatstore for DHW is satisfied. Likewise, while you are running a bath or shower, you will get no heating. This is the way the boiler is designed to work.
 
The boiler will most likely be recharging its internal hot water storage when it doesn't give you instant heat to the radiators; this ensures that you have instant hot water available for your taps at all times
 
Very sensible for those who must have a combi.

But I would always recommend a proper boiler and cylinder for anything larger than a small flat.

Tony
 
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Your boiler will always give priority to hot water. If the boiler is cold, then when switched on, you will get no heating until the heatstore for DHW is satisfied. Likewise, while you are running a bath or shower, you will get no heating. This is the way the boiler is designed to work.

Hi Oilhead

The combi is always switched on at the mains electric plug in the garage and can frequently be seen burning when there is no one in the house, and no one has been in the house for a long time, to recharge the hot water store. Is it possible the expansion vessel within the boiler is burst and needs replacing? This was replaced once before and I forget the reason.
 
If you don't want the boiler to preheat its internal water storage, then you can usully turn this feature off. Check the manual. Sometimes it's called the "eco" or "green" option, or whatever.
 
Your boiler will always give priority to hot water. If the boiler is cold, then when switched on, you will get no heating until the heatstore for DHW is satisfied. Likewise, while you are running a bath or shower, you will get no heating. This is the way the boiler is designed to work.

Hi Oilhead

The combi is always switched on at the mains electric plug in the garage and can frequently be seen burning when there is no one in the house, and no one has been in the house for a long time, to recharge the hot water store. Is it possible the expansion vessel within the boiler is burst and needs replacing? This was replaced once before and I forget the reason.
Nothing to do with the expansion vessel - it's just that the stored hot water cools down then has to be reheated. It should be possible to put a timer on it. If you're away a lot, you might want to fit a Nest to it...
 
Your boiler will always give priority to hot water. If the boiler is cold, then when switched on, you will get no heating until the heatstore for DHW is satisfied. Likewise, while you are running a bath or shower, you will get no heating. This is the way the boiler is designed to work.

Hi Oilhead

The combi is always switched on at the mains electric plug in the garage and can frequently be seen burning when there is no one in the house, and no one has been in the house for a long time, to recharge the hot water store. Is it possible the expansion vessel within the boiler is burst and needs replacing? This was replaced once before and I forget the reason.
Nothing to do with the expansion vessel - it's just that the stored hot water cools down then has to be reheated. It should be possible to put a timer on it. If you're away a lot, you might want to fit a Nest to it...
Aw FFS. Queue the " how do I wire a Nest into my ...,,," thread coming up:D
 
I reckon I've got a pretty good tutorial on here now...maybe it should be a Sticky!
 
Your boiler will always give priority to hot water. If the boiler is cold, then when switched on, you will get no heating until the heatstore for DHW is satisfied. Likewise, while you are running a bath or shower, you will get no heating. This is the way the boiler is designed to work.

Hi Oilhead

The combi is always switched on at the mains electric plug in the garage and can frequently be seen burning when there is no one in the house, and no one has been in the house for a long time, to recharge the hot water store. Is it possible the expansion vessel within the boiler is burst and needs replacing? This was replaced once before and I forget the reason.
Nothing to do with the expansion vessel - it's just that the stored hot water cools down then has to be reheated. It should be possible to put a timer on it. If you're away a lot, you might want to fit a Nest to it...
Aw FFS. Queue the " how do I wire a Nest into my ...,,," thread coming up:D

Shambolic,
I don't need a NEST, though had you not 'prompted' I might have had to think, 'what is that'?
I modified my Honeywell CM927 wireless timing / controller switch; I added some electronic components (a NodeMCU, a songle relay and a 240ac to 5v dc power supply) and can now switch it on remotely from my phone anywhere.
 
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