Problem with megaflo hot water cylinder?

dharm999

ComicGeek said:

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).

The pump runs when there is any draw, hot or cold, and regardless of outlet, so it can be a tap, toilet, or shower 

Yes, there are two tanks in the loft

Will ask my plumber to have a look at reducing the target pressure.  

I have investigated further following the comments and I think there are two different things going on.  One is the issue with the pump.  The other is a possible boiler problem.  The boiler is a Greenstar 40cdi classic regular, which has had the heat exchanger recently changed.   When the boiler temperature drops to around 55 it kicks in, the temperature increases to c65 and then it stops.  The temp drops again and then it kicks in again.  I think it’s simply a coincidence that this appears to cause the pump to start.  The pump starting sometimes coincides with the boiler kicking in, as it doesn’t always run at the same time the boiler does.

The boiler has a little icon on the panel, that looks like a suitcase with a sun to the right of it, I’m guessing thats a holiday mode? The light to the left of this icon is on, and green , could that be causing the boiler to regularly start, to maintain a certain temperature or is this just the standard way it runs?

The boiler doesn’t fire up when drawing hot water.

Apologies if previous answers have confused matters, not my intention.

Albermarle

When the boiler temperature drops to around 55 it kicks in, the temperature increases to c65 and then it stops.  The temp drops again and then it kicks in again

This would be normal for an older boiler. They only have two heat settings - on at fullblast, or off . So they will keep turning on and off to keep the water temperature within a certain range. A newer boiler will turn itself up and down, rather than on and off.

Yes, there are two tanks in the loft

One of the advantages of a Megaflow system, is you do not need any tanks in the loft, so the plot thickens.....

dharm999

The two tanks are cold water tanks, toAlbermarle said:

When the boiler temperature drops to around 55 it kicks in, the temperature increases to c65 and then it stops.  The temp drops again and then it kicks in again

This would be normal for an older boiler. They only have two heat settings - on at fullblast, or off . So they will keep turning on and off to keep the water temperature within a certain range. A newer boiler will turn itself up and down, rather than on and off.

Yes, there are two tanks in the loft

One of the advantages of a Megaflow system, is you do not need any tanks in the loft, so the plot thickens.....

There is a dial  that goes from 1 to 6, I assume I use that to control when the boiler kicks in?

Is there a rational reason to have the cold water tanks in the loft?  Could it be linked to having the pump, so that the two combined ensure a decent level of water pressure to the various outlets?

dharm999

Forgot to say, there is no thermostat at the top or bottom levels, where there is radiator heating, so I assume the heating stays on for the length of time it is set up for in the control panel rather than going off when the required room temperature is reached.

ComicGeek

dharm999 said:

ComicGeek said:

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).

The pump runs when there is any draw, hot or cold, and regardless of outlet, so it can be a tap, toilet, or shower 

Yes, there are two tanks in the loft

Will ask my plumber to have a look at reducing the target pressure.  

I have investigated further following the comments and I think there are two different things going on.  One is the issue with the pump.  The other is a possible boiler problem.  The boiler is a Greenstar 40cdi classic regular, which has had the heat exchanger recently changed.   When the boiler temperature drops to around 55 it kicks in, the temperature increases to c65 and then it stops.  The temp drops again and then it kicks in again.  I think it’s simply a coincidence that this appears to cause the pump to start.  The pump starting sometimes coincides with the boiler kicking in, as it doesn’t always run at the same time the boiler does.

The boiler has a little icon on the panel, that looks like a suitcase with a sun to the right of it, I’m guessing thats a holiday mode? The light to the left of this icon is on, and green , could that be causing the boiler to regularly start, to maintain a certain temperature or is this just the standard way it runs?

The boiler doesn’t fire up when drawing hot water.

Apologies if previous answers have confused matters, not my intention.

So does sound like the pump is on the cold water side. What is your water pressure like out of the taps, and does this vary between floors? If you can get to the Grundfos pump make a note of the model number on the front - will be something like UPA 15-90, but is helpful in working out the purpose of the pump. 

The Greenstar CDi classic regular boilers could be installed as open vented or sealed, so possible that one of the loft tanks is the expansion tank for the heating system.

But is your hot water cylinder actually a Megaflo (brand name), or is it a different manufacturer? List the cylinder make and model here. An older vented cylinder would have a header tank in the loft, an unvented cylinder would have a red expansion vessel near to the cylinder - Megaflo (as a specific brand name) have an internal air bubble instead of a separate expansion vessel. If the second loft tank is actually the cylinder header tank, then your water pump in the loft could be a home booster pump, which just pumps directly from the main.

dharm999

The boiler has a separate expansion tank next to it, fixed to the wall.

Definitely a megaflo as it has it written on it.

Will find out model numbers tomorrow and post those

dharm999

The megaflo is a CL300, and next to it is another grundfoss pump, ups15-60, which I am guessing is for the underfloor heating as it is next to the various UFH pipes.

What I still can’t quite understand is why the pump in the loft comes on every 2-3 minutes at night when there is no draw, no heating or hot water on, and the boiler isn’t kicking in.  If it’s meant to ensure a certain amount of water pressure, does that suggest there is a ‘leak’, for want of a better word, that results in the pump starting to maintain the pressure.  And why is the intervals of time when it comes on, so much longer in the day compared to at night?  I can only assume that as there is a frequent draw on water during the day the pump is working very regularly and so the pressure is maintained because of the usage, and there is less opportunity for the pressure to drop and the pump to kick back in to maintain the pressure it has been set up for.

Or am I completely wrong, and it’s something else?

Albermarle

dharm999 said:

The megaflo is a CL300, and next to it is another grundfoss pump, ups15-60, which I am guessing is for the underfloor heating as it is next to the various UFH pipes.

What I still can’t quite understand is why the pump in the loft comes on every 2-3 minutes at night when there is no draw, no heating or hot water on, and the boiler isn’t kicking in.  If it’s meant to ensure a certain amount of water pressure, does that suggest there is a ‘leak’, for want of a better word, that results in the pump starting to maintain the pressure.  And why is the intervals of time when it comes on, so much longer in the day compared to at night?  I can only assume that as there is a frequent draw on water during the day the pump is working very regularly and so the pressure is maintained because of the usage, and there is less opportunity for the pressure to drop and the pump to kick back in to maintain the pressure it has been set up for.

Or am I completely wrong, and it’s something else?

It sounds like you are on the right track.
Normally with a megaflow there are no tanks in the loft, as it runs directly off mains pressure.
However if your local mains pressure is not very good, then the system will struggle to deliver hot or cold water to more than one outlet at a good pressure.
So what is in the loft and the pump are there to maintain a higher water pressure. Just guessing though.

dharm999

I’m not now sure what my next steps are.  I need to find out what pump is in the loft, but once I know that, what next?  Get my plumber to turn down the pressure the pump,is set for, and see if that makes a difference to how often the pump comes on at night?  How to track down what is causing the pressure to drop that is causing the pump to kick in?  Where do I start with that? 

dharm999

A;so, if the boiler is set up for ‘holiday mode’, how do I switch that off, as I want to make sure that everything is set up for normal running to get a base line that I can compare against.