Header tank over flowing

[andy-man]

I have an issue with our open vented heating system.
The system was fitted around 7 years ago and has worked with no issues.
I have just fitted 4 new designer rads and a heated towel rail. Re filled and bled the system, and balanced the rads. The issue i have is, when the boiler turns off, water comes out of the header tank.
I have tried turning the pump down as I thought it was drawing air in via the vents pipe. But it's made no difference. Live in a bungalow so the header tank is only about 3 foot above the boiler.
Never had an issue before fitting the vertical rads.
Could they be the issue.

Andy

 

[CountryFan]

Have you checked if the float valve is operating correctly? Could be as simple as that.

 

[Johntheo5]

I have an issue with our open vented heating system.
The system was fitted around 7 years ago and has worked with no issues.
I have just fitted 4 new designer rads and a heated towel rail. Re filled and bled the system, and balanced the rads. The issue i have is, when the boiler turns off, water comes out of the header tank.
I have tried turning the pump down as I thought it was drawing air in via the vents pipe. But it's made no difference. Live in a bungalow so the header tank is only about 3 foot above the boiler.
Never had an issue before fitting the vertical rads.
Could they be the issue.

A

Can you see what type of vent & cold feed arrangement you have, you don't say whether oil or gas fired with external circ pump?, your system may look something like the attached (close coupled) where from the boiler flow, you have the Vent then the Cold feed (no more than 150mm from the vent) and then the circ pump, also post make/model/setting of the circ pump.

 

[andy-man]

Gas boiler, and close coupled as above.
it's a Grunfoss UPS3 set a speed 1.
Never had an issue in 7 / 8 years. Its only happened since I fitted some vertical tube designer radiators.
The boiler is an Ideal heat 24. I have noticed it only happens if the boiler is on and the timer turns off. The pump stops, as far as I can see from the wiring diagram. There is no way the pump can run, as it takes its feed from the orange wires on the 2 zone valves.

 

[Johntheo5]

It is very unusual with a gas fired boiler not to have pump overrun + a ABV (automatic bypass valve) for a a few minutes when the boiler stops, the pump would then be fed from the boiler, most of which hve the facility to provide power to the pump for this overrun time, however you have lived without it for years.

You say water comes out of the header tank, is this through the overflow?, does it only happen for a minute or so after the pump stops, is there any pump over through the vent?. Get someone to start the boiler via CH timer/roomstat while you watch the vent and see does it vent water through the vent for a few seconds and again keep viewing it while getting them to switch off the boiler.

A few other things you might try is, first, with the system shut down, just manually latch open the cylinder zone valve and ensure that the boiler does not start, I know that Honeywell zone valves do not close the auxiliary switch which fires the boiler but EPH do, others may do so as well, if the boiler does not start, then ensure HW programmed off...then latch its zone valve open, run the boiler for say 15 minutes or so on CH, then switch off and see do you still get overflow.
Secondly, you might change the pump speed to CP1, (constant pressure), which means the pump will run with a 3.0M head vs 4.2M and see does it make any difference, 3.0M should probably still be OK to circulate your system but see what happens anyway if you do those tests.

 

[danfre]

S plan, no bypass

 

[andy-man]

S plan, no bypass

S plan, and bypass.

 

[andy-man]

It is very unusual with a gas fired boiler not to have pump overrun + a ABV (automatic bypass valve) for a a few minutes when the boiler stops, the pump would then be fed from the boiler, most of which hve the facility to provide power to the pump for this overrun time, however you have lived without it for years.

You say water comes out of the header tank, is this through the overflow?, does it only happen for a minute or so after the pump stops, is there any pump over through the vent?. Get someone to start the boiler via CH timer/roomstat while you watch the vent and see does it vent water through the vent for a few seconds and again keep viewing it while getting them to switch off the boiler.

A few other things you might try is, first, with the system shut down, just manually latch open the cylinder zone valve and ensure that the boiler does not start, I know that Honeywell zone valves do not close the auxiliary switch which fires the boiler but EPH do, others may do so as well, if the boiler does not start, then ensure HW programmed off...then latch its zone valve open, run the boiler for say 15 minutes or so on CH, then switch off and see do you still get overflow.
Secondly, you might change the pump speed to CP1, (constant pressure), which means the pump will run with a 3.0M head vs 4.2M and see does it make any difference, 3.0M should probably still be OK to circulate your system but see what happens anyway if you do those tests.

I can answer a few questions. We are away now for a few days, so will have to try the others when we are back.
Unfortunately an Ideal heat only boiler doesn't have the facility for pump overrun. Unless you by a pump overrun module.
Yes, water flows out of the overflow for 30 seconds or so after the boiler stops. But it only happens when the programmer switches the boiler off at the set heating off time.
If I manually latch the valve open, the boiler doesn't start.
A couple of things re the pump. Its always been set at speed 3. Now if it's on 3 there's a noticeable know when the boiler turns off.

Thanks for all the advice

 

[denso13]

If it is pumping over, just as it shuts down, then probably a restriction/blockage at the feed/expansion connection. A common problem.