Repressurising a sealed boiler with low mains pressure

carveone

Hi all,

I have a Potterton System boiler. The hotpress has a mass of plastic pipe (urgh) connected to a hot & cold pump. The previous owner took a tap off the hot water side of the pump outlet, via a isolation valve and a non-return valve, to the heating system. This is used to repressurise the boiler if the pressure drops out (which it had when I moved in).

Is the only reason to do this low mains water pressure? If the incoming mains feed to ones apartment is less than 1.5 bar, is a pump the only way of repressurising an unvented boiler? 1.5 bar is 15m of head so I suppose I can't do it off the attic tank!

The bathroom and kitchen water pressure without the pump on is fine as far as I'm concerned - there's a header tank in the attic. Besides, the pump is screechy as hell - bearings are going... Cold water at the kitchen tap seems ok. I guess if I could measure the pressure there I'd know more (15m of pipe out the window straight up maybe )

Dtp1979

carveone wrote: »

Hi all,

I have a Potterton System boiler. The hotpress has a mass of plastic pipe (urgh) connected to a hot & cold pump. The previous owner took a tap off the hot water side of the pump outlet, via a isolation valve and a non-return valve, to the heating system. This is used to repressurise the boiler if the pressure drops out (which it had when I moved in).

Is the only reason to do this low mains water pressure? If the incoming mains feed to ones apartment is less than 1.5 bar, is a pump the only way of repressurising an unvented boiler? 1.5 bar is 15m of head so I suppose I can't do it off the attic tank!

The bathroom and kitchen water pressure without the pump on is fine as far as I'm concerned - there's a header tank in the attic. Besides, the pump is screechy as hell - bearings are going... Cold water at the kitchen tap seems ok. I guess if I could measure the pressure there I'd know more (15m of pipe out the window straight up maybe )

It's no harm re pressurising the heating from the pump. It should have no real effect on the pump as the heating should only need to be topped up a couple of times a year maybe

carveone

Dtp1979 wrote: »

It's no harm re pressurising the heating from the pump. It should have no real effect on the pump as the heating should only need to be topped up a couple of times a year maybe

I understand but it does pain me to look at the mess of qualplex connected to a pump I don't want to use! If I don't look at it I guess I can live with it If I replace the boiler at some point (possibly sooner than later given the amount of scaling the boiler guy said was in it - it's kettling a bit) than I might need to know if I can chuck the pump. Which means knowing if the mains pressure is adequate to pressurise the boiler. Thanks...

Dtp1979

carveone wrote: »

I understand but it does pain me to look at the mess of qualplex connected to a pump I don't want to use! If I don't look at it I guess I can live with it If I replace the boiler at some point (possibly sooner than later given the amount of scaling the boiler guy said was in it - it's kettling a bit) than I might need to know if I can chuck the pump. Which means knowing if the mains pressure is adequate to pressurise the boiler. Thanks...

If it's only aesthetics that's bothering you then have it changed. Water from the pump isn't gonna damage your boiler unless your constantly topping up the pressure constantly

Calahonda52

If replacing, pick one that doesn't need a min of even 0.5 bar which I think that one is.
I take it the pump is for de shower only

nmacc

It's not a good idea generally to connect the filling loop to the output of a shower pump. If the systems pressure is very low then it will work fine, however because the pump is triggered by flow, it may not top up when the heating system is only a little less than you might wish.

I had this problem previously with a system plumbed this way and changed it over to the mains.

Having said that, if it's working at the moment, then all's well and good.

Calahonda52

nmacc wrote: »

It's not a good idea generally to connect the filling loop to the output of a shower pump. If the systems pressure is very low then it will work fine, however because the pump is triggered by flow, it may not top up when the heating system is only a little less than you might wish.

I had this problem previously with a system plumbed this way and changed it over to the mains.

Having said that, if it's working at the moment, then all's well and good.

Good point there, so the next idea is that if he cuts the power to the pump, as its an impeller pump, the static head from the attic tank may get him over the line?

nmacc

Calahonda52 wrote: »

Good point there, so the next idea is that if he cuts the power to the pump, as its an impeller pump, the static head from the attic tank may get him over the line?

Not impossible, but personally I doubt it, unless it's a very long way to the attic. Don't forget that 1 Bar represents 10 metres (or three storeys) of head.

K.Flyer

If the pump will not activate to bring up the pressure, just open a tap on the other line, in the O.P.'s case, it would be a cold tap, this activates the pump, leave it running, open the filling valve, reach the desired pressure on the boiler and close all taps and valves.

carveone

K.Flyer wrote: »

If the pump will not activate to bring up the pressure, just open a tap on the other line, in the O.P.'s case, it would be a cold tap, this activates the pump, leave it running, open the filling valve, reach the desired pressure on the boiler and close all taps and valves.

(hot tap in this case). That's exactly what I do but I cannot see the pressure valve on the boiler from the hotpress so I do it the opposite way round - open valve, then open the tap.

I was concerned that overpressure from the pump might damage the boiler. But so far I've been fine - it kicks up to 1.2bar max. I've had to repressurise twice in two weeks but that might just be because the system has been sitting for 18 months (crossing fingers that there's no leak)

I believe that the pump in the hotpress was put in solely for the boiler as the shower has its own pump with a surrey flange into the hot water tank. The pressure at the sinks is ok, more or less, with the pump off. The pump is on the way out so I leave it off.

As nmacc says I have to run a tap to trigger the pump. I open the cross valve, go into the kitchen where the boiler is and run the hot tap. Only takes a few seconds.

nmacc wrote:

I had this problem previously with a system plumbed this way and changed it over to the mains.

That's what I want to do but first step would be to measure the mains pressure at the kitchen tap. The attic is only 2m above that so that's not enough head. I don't know any alternative if you don't have enough mains pressure. Hand pump maybe

Calahonda52

carveone wrote: »

Hi all,

I have a Potterton System boiler. The hotpress has a mass of plastic pipe (urgh) connected to a hot & cold pump. The previous owner took a tap off the hot water side of the pump outlet, via a isolation valve and a non-return valve, to the heating system. This is used to repressurise the boiler if the pressure drops out (which it had when I moved in).

Is the only reason to do this low mains water pressure? If the incoming mains feed to ones apartment is less than 1.5 bar, is a pump the only way of repressurising an unvented boiler? 1.5 bar is 15m of head so I suppose I can't do it off the attic tank!

The bathroom and kitchen water pressure without the pump on is fine as far as I'm concerned - there's a header tank in the attic. Besides, the pump is screechy as hell - bearings are going... Cold water at the kitchen tap seems ok. I guess if I could measure the pressure there I'd know more (15m of pipe out the window straight up maybe )

and

carveone wrote:

I believe that the pump in the hotpress was put in solely for the boiler as the shower has its own pump with a surrey flange into the hot water tank. The pressure at the sinks is ok, more or less, with the pump off. The pump is on the way out so I leave it off.

Find that hard to understand in the context of a tap off in your first post?
Any pics?

Egass13

If your getting over 1 bar from the pump , what exactly is the issue ?

Egass13

If your getting over 1 bar from the pump , what exactly is the issue ?

Dtp1979

Egass13 wrote: »

If your getting over 1 bar from the pump , what exactly is the issue ?

It dosent look nice

carveone

Calahonda52 wrote: »

and

Find that hard to understand in the context of a tap off in your first post?
Any pics?

I don't have a digital camera unfortunately. But that was a misuse of the word tap, sorry. I meant a T junction, that's all. The hot outlet from the pump goes to a T which continues to the hot feed...

There currently isn't any issue as such. It's fine for the moment. The original question was just whether there's any other way of dealing with this (than a pump) if the mains pressure is too low. I thought there might be some magic hand pump thing. The answer appears to be no though, which is ok...

Wearb

You could use a barrel pump or similar to top it up.

Egass13

carveone wrote: »

I don't have a digital camera unfortunately. But that was a misuse of the word tap, sorry. I meant a T junction, that's all. The hot outlet from the pump goes to a T which continues to the hot feed...

There currently isn't any issue as such. It's fine for the moment. The original question was just whether there's any other way of dealing with this (than a pump) if the mains pressure is too low. I thought there might be some magic hand pump thing. The answer appears to be no though, which is ok...

Surely mains would be sufficient , that boilers flowswitch activates at .2 of a bar although it says min requirement is .5 of a bar .

carveone

Egass13 wrote: »

Surely mains would be sufficient , that boilers flowswitch activates at .2 of a bar although it says min requirement is .5 of a bar .

You're almost certainly right. It does say 0.5 bar minimum but it still works at lower than that. If I check the mains pressure I can get it redone at some point. Thanks.