Combi boiler- running a cold tap knocks the heating off?
Discussion
Afternoon folks
We have a fairly recent Worcester Bosch combi boiler. I've noticed that when the central heating is switched on any use of a cold tap knocks it off and it takes at least a minute to kick back in again.
When the washing machine was filling earlier the boiler took forever to finally kick back in and start heating again.
Is this normal? I know the hot tap would over ride the heating but it's a right pain if the cold does the same!
We have a fairly recent Worcester Bosch combi boiler. I've noticed that when the central heating is switched on any use of a cold tap knocks it off and it takes at least a minute to kick back in again.
When the washing machine was filling earlier the boiler took forever to finally kick back in and start heating again.
Is this normal? I know the hot tap would over ride the heating but it's a right pain if the cold does the same!
Lincsls1 said:
Eh? That has nothing to do with the heating control.
Yes, I think it does. Our W-B combi used to do exactly the same. I suspect there is a pressure sensor in the DHW side of the boiler and if it drops below the cutoff level, it shuts the flame down for protection even if DHW isn't being used.With ours, also, the bigger mystery was why the CH pressure gauge would fluctuate when the cold water tap was turned on suddenly. I never understood how the sealed loop side of the CH could react like this.
Nope, there is no 'pressure' sensor on the HW circuit. Just a flow sensor.
Many WB boilers don't even have system pressure sensors, and will run with '0' on the pressure happily enough.
The latest ones do though, like the Lifestyle range for example, but again this has nothing to do with the HW circuit.
It is a mystery. I'm just wondering if somehow when a cold tap is run, or moreover turned off, the 'back lash' through pipework might just trigger the hot water flow switch, very briefly, causing the boiler to stop the heating, which triggers an anti-cycle type timer before the heating kicks in again.
I wonder if a surge arrester would cure it.
Many WB boilers don't even have system pressure sensors, and will run with '0' on the pressure happily enough.
The latest ones do though, like the Lifestyle range for example, but again this has nothing to do with the HW circuit.
It is a mystery. I'm just wondering if somehow when a cold tap is run, or moreover turned off, the 'back lash' through pipework might just trigger the hot water flow switch, very briefly, causing the boiler to stop the heating, which triggers an anti-cycle type timer before the heating kicks in again.
I wonder if a surge arrester would cure it.
Lincsls1 said:
Nope, there is no 'pressure' sensor on the HW circuit. Just a flow sensor.
Many WB boilers don't even have system pressure sensors, and will run with '0' on the pressure happily enough.
The latest ones do though, like the Lifestyle range for example, but again this has nothing to do with the HW circuit.
It is a mystery. I'm just wondering if somehow when a cold tap is run, or moreover turned off, the 'back lash' through pipework might just trigger the hot water flow switch, very briefly, causing the boiler to stop the heating, which triggers an anti-cycle type timer before the heating kicks in again.
I wonder if a surge arrester would cure it.
That's an interesting idea thanks. Due a service in the new year so I'll get the plumber to investigate and see if this could be a solution. Many WB boilers don't even have system pressure sensors, and will run with '0' on the pressure happily enough.
The latest ones do though, like the Lifestyle range for example, but again this has nothing to do with the HW circuit.
It is a mystery. I'm just wondering if somehow when a cold tap is run, or moreover turned off, the 'back lash' through pipework might just trigger the hot water flow switch, very briefly, causing the boiler to stop the heating, which triggers an anti-cycle type timer before the heating kicks in again.
I wonder if a surge arrester would cure it.
Most frustrating as it makes heating up a cold Edwardian house pretty slow unless you ban the family from touching the taps for the first hour!
Another check is to turn a cold tap on/off when the heating is not on. You will probably hear the boiler fan kick in.
As mentioned above it is sensing a pressure blip on the hot side which is what triggers the boiler to fire in hot water mode. If the heating is on it shuts off the heating and switches to hot water. If you run a bath the heating won't be on until the bath is filled and there is no longer a hot water demand.
You can usually cure it by installing a shock arrester in the supply pipework, It's good practice anyway to fit one with a new combi.
https://www.screwfix.com/p/flomasta-vessel-shock-a...
As mentioned above it is sensing a pressure blip on the hot side which is what triggers the boiler to fire in hot water mode. If the heating is on it shuts off the heating and switches to hot water. If you run a bath the heating won't be on until the bath is filled and there is no longer a hot water demand.
You can usually cure it by installing a shock arrester in the supply pipework, It's good practice anyway to fit one with a new combi.
https://www.screwfix.com/p/flomasta-vessel-shock-a...
TT86 said:
Lincsls1 said:
Nope, there is no 'pressure' sensor on the HW circuit. Just a flow sensor.
Many WB boilers don't even have system pressure sensors, and will run with '0' on the pressure happily enough.
The latest ones do though, like the Lifestyle range for example, but again this has nothing to do with the HW circuit.
It is a mystery. I'm just wondering if somehow when a cold tap is run, or moreover turned off, the 'back lash' through pipework might just trigger the hot water flow switch, very briefly, causing the boiler to stop the heating, which triggers an anti-cycle type timer before the heating kicks in again.
I wonder if a surge arrester would cure it.
That's an interesting idea thanks. Due a service in the new year so I'll get the plumber to investigate and see if this could be a solution. Many WB boilers don't even have system pressure sensors, and will run with '0' on the pressure happily enough.
The latest ones do though, like the Lifestyle range for example, but again this has nothing to do with the HW circuit.
It is a mystery. I'm just wondering if somehow when a cold tap is run, or moreover turned off, the 'back lash' through pipework might just trigger the hot water flow switch, very briefly, causing the boiler to stop the heating, which triggers an anti-cycle type timer before the heating kicks in again.
I wonder if a surge arrester would cure it.
Most frustrating as it makes heating up a cold Edwardian house pretty slow unless you ban the family from touching the taps for the first hour!
I had that with a new compact wb combi replacing a system boiler, luckily i noticed on the night after installation and the heating engineer was due back the next day, he fit a check valve inline ( i cant remember which pipe, cold water feed i think) to fix it. Said it was something to do with a new water meter? Didn’t believe him but it worked, that was approx 15 years ago.
New boiler this year in a different house has a surge arrestor fitted from the start.
New boiler this year in a different house has a surge arrestor fitted from the start.
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