Problem with megaflo hot water cylinder?

dharm999

Moved in to our house a few weeks ago.  There is a system boiler and megaflo hot water tank.  House is three floors.  Bottom floor has traditional radiators heating.  Middle floor has underfloor heating with each room having its own control.  Top floor has a combination of UFH in the bathrooms and radiators in the bedrooms.

Boiler has two control panels, one is for heating only and the other is for heating and hot water.  There is a grundfoss pump in the attic that comes on when there is a draw on water anywhere in the house, be it a tap , shower, bath or toilet flush.

We haven’t had the heating on so far using the control panels on the boiler, we’ve been using the room controls for the UFH ad and when we need to.  The hot water is on twice a day for an hour each time

The problem is that the pump comes on periodically when there is no apparent draw on water.  When it comes on, the boiler kicks in for about 10 seconds, the temperature on it increases by 5-6 degrees, and the pump comes on for about 10 seconds.  During the day the interval of time between the pump coming on can be anywhere up to 10 minutes.  At night when we go to sleep, the pump kicks in every 2 minutes.

My thinking is that there may be a problem with the megaflo, as the heating isn’t on very often, and during the day we use hot water regularly, so are drawing on it from the megaflo.  But at night as we aren’t using it, the pump kicks in every 2 minutes.  Is my thinking right, if so, what could be wrong with it?  If not, what else do I need to look at?

To add, the UFH at the top level is set to winter setting so hasn’t yet come on, so it’s not that causing the pump to kick in at night.  I’ve made sure all taps are closed and no toilets have a slow trickle of water in to the pan.

Does anyone have any ideas, as it’s driving me to distraction, as well as increasing gas use and strain on the pump

Thanks

nofoollikeold

1. Picture of the pump and controls?
2. If it is a secondary circulation pump (bronze coloured or stainless steel body) it should only run if hot water is used.  Normally though they run all the time except when turned off on a timer / PIR / other controller.  If this is the problem, turn it off at the mains overnight.  Will then take longer for hot water to reach taps.
3. If it's a shower type pump, its shouldn't be fitted to an unvented cylinder.  
4. If it's a central heating circulation pump, it shouldn't be needed with a system boiler.

dharm999

nofoollikeold said:

1. Picture of the pump and controls?
2. If it is a secondary circulation pump (bronze coloured or stainless steel body) it should only run if hot water is used.  Normally though they run all the time except when turned off on a timer / PIR / other controller.  If this is the problem, turn it off at the mains overnight.  Will then take longer for hot water to reach taps.
3. If it's a shower type pump, its shouldn't be fitted to an unvented cylinder.  
4. If it's a central heating circulation pump, it shouldn't be needed with a system boiler.

Thanks.  My plumber said that he thought it had been installed to maintain water pressure to the various outlets.  I asked him to give the overall system a once over when we moved in, and the problem wasn’t apparent then.  It’s a grundfoss pump.

The pump is in the loft, so not easy to get a picture, but will try and get one and post it.

It only runs when there is a draw on water, you can hear it kick in.

What would I look for to identify if it’s a shower type or central heating type?

RavingMad

Could you turn the boiler off? See if it kicks in then?

My suggestion is from next to no understanding on how CH works so I'm fully expecting someone to say that's nonsense  but didn't want that thought to go to waste   

FreeBear

dharm999 said: The problem is that the pump comes on periodically when there is no apparent draw on water.  When it comes on, the boiler kicks in for about 10 seconds, the temperature on it increases by 5-6 degrees, and the pump comes on for about 10 seconds.  During the day the interval of time between the pump coming on can be anywhere up to 10 minutes.  At night when we go to sleep, the pump kicks in every 2 minutes.

It sounds like the pump is kicking in to circulate hot water around the system so that you don't have to wait when turning on a tap. Is the hot water pipe under each sink hot to touch ?

If so, this is the answer to your problem, and I would expect there to be some option on the control panel to disable this "feature". Turn it off, and you'll save gas (and money) at the expense of having to wait for hot water to come out of the tap.

ComicGeek

If it's on the cold water pipework then shouldn't turn boiler on. Are you sure that the pump runs when just the toilet is flushed?

Check the pipe either side of the pump to see if it's cold or hot. Is there a cold water tank up there as well?

3 storeys plus loft would need really good mains water pressure. If the pump is on the cold water pipework see if there is a setting to reduce the target water pressure - possible that it's just not possible to maintain the target static (taps off) and dynamic (taps on) water pressure hence the pump running all the time.  

But shouldn't be any interaction between cold water pressure and heating system, unless hot water is being drawn off from the Megaflo somewhere and the cylinder heating is set to constantly on (ie the boiler fires up to reheat the Megaflo as soon as any hot water is drawn off).

Albermarle

nofoollikeold said:

1. Picture of the pump and controls?
2. If it is a secondary circulation pump (bronze coloured or stainless steel body) it should only run if hot water is used.  Normally though they run all the time except when turned off on a timer / PIR / other controller.  If this is the problem, turn it off at the mains overnight.  Will then take longer for hot water to reach taps.
3. If it's a shower type pump, its shouldn't be fitted to an unvented cylinder.  
4. If it's a central heating circulation pump, it shouldn't be needed with a system boiler.

Not sure Point 4 is correct. How does the central heating water get around the system without a pump ? Or are you assuming there is a pump integrated in the boiler ( that is not always the case).

Albermarle

OP.
The 'normal' set up is that you heat the water in the Megaflow cylinder. When you turn on a hot tap, the mains pressure in the system delivers the hot water to the tap, with no pump involved. If you leave the tap on, eventually the hot water runs out. Then you need to switch the boiler on again to heat more hot water.
There will be a pump next to or integrated with the boiler, which will operate only when the boiler is operating.

Normally there is not another pump for these systems, so it sounds like your set up is some kind of bespoke job, which is probably why other posters are having to guess what might be happening.

FreeBear

Albermarle said: Normally there is not another pump for these systems, so it sounds like your set up is some kind of bespoke job, which is probably why other posters are having to guess what might be happening.

Not normally, I agree. But there could be a pump in the DHW pipe to recirculate hot water. See - https://www.bolasystems.com/help-advice/dhw-circulator-pumps - Note the pump & return pipe on the hot side.

nofoollikeold

The OP stated that the pump runs on a toilet flush.  This suggests to me it is not a hot water circulating pump, although I have seen normal WC's plumbed into the hot pipework on new builds.  

dharm999

FreeBear said:

dharm999 said: The problem is that the pump comes on periodically when there is no apparent draw on water.  When it comes on, the boiler kicks in for about 10 seconds, the temperature on it increases by 5-6 degrees, and the pump comes on for about 10 seconds.  During the day the interval of time between the pump coming on can be anywhere up to 10 minutes.  At night when we go to sleep, the pump kicks in every 2 minutes.

It sounds like the pump is kicking in to circulate hot water around the system so that you don't have to wait when turning on a tap. Is the hot water pipe under each sink hot to touch ?

If so, this is the answer to your problem, and I would expect there to be some option on the control panel to disable this "feature". Turn it off, and you'll save gas (and money) at the expense of having to wait for hot water to come out of the tap.

No, the pipes are cold to the touch