Best setting for Grundfos UPS3 pump - open vented CH system

[ukmark62]

Hi,

Just trying to understand our new pump a little more and I'm no expert to say the least on CH matters.

System is open vented with larger cold storage tank and smaller expansion tank in loft. Boiler is Ideal Icos HE18. We have 6 "normal" radiators (3 up, 3 down) plus a towel radiator in the bathroom - so 7 in total. We also have a hot water cylinder in the upstairs airing cupboard and the new Grundfos UPS3 pump is in the same airing cupboard just above the flooring and below the cylinder tank. TRVs on 6 "normal" radiators and the towel radiator is almost fully open on both the inflow and outflow valves. Boiler flow temp for radiators is set at around 50 degrees C (there is no temp setting for hot water). This was also recommended by the central heating team who powerflushed the radiators a few months ago. Prior to that it was around 65-70 degrees C (not exact as the boiler does not have a digital readout - only a numberless dial with min and max - the range of the dial is apparently 30-82 degrees C.) I think we have a two-pipe system. I don't know if we have any "auto bypass valves".

We had the system powerflushed and inhibitor added a few months ago along with TRVs added to the 6 radiators. Engineer did note that our radiators were in very good condition - the existing water in the radiators prior to flushing was quite clean.

Everything is working almost perfectly. We did have the pump replaced, as prior to this, we experienced some random banging noises and hot water going up the vent pipe into the expansion tank and subsequently causing more air in the radiators. The only question I have is what is the best setting for the UPS3 pump. I am by no means familiar with the terminology mentioned in the Grundfos documentation.

There are "constant curve" settings (1,2 and 3).
There are "proportional pressure" settings (low and high)
There are "constant pressure" settings (low and high)

Currently the pump is on "constant curve" 2 - this was the setting chosen by the installer a few weeks ago. We occasionally still get slight expansion of water through the vent pipe in the loft into the expansion tank, but nowhere near like it was with the old pump - so far once per day, but not much water. I'm reluctant to try different speed settings without an understanding or appreciation if they will improve things or not. The pump is quiet and all radiators get warm.

We would love to have zero water expansion into the expansion tank if possible - is that possible, or is it inevitable that some water will always end up in the expansion tank from the vent pipe?

Is it fair to say that if the pump speed is too slow, this will cause boiler to overheat (make some knocking and clanging noises) and then this could cause the water to overflow from the vent pipe into expansion tank and then cause more air in radiators? This seemed to happen when we had the old faulty pump - the return pipe on the boiler was always cold whilst the flow pipe was always hot. The boiler would start making strange noises for a few seconds and then we would get water up the vent pipe.

Any help/advice would be appreciated.

 

[Johntheo5]

You shouldn't get any expansion into the F&E cistern, its certainly not inevitable.
The UPS3 is one of the most powerful 6M circ pumps you can get, CC2 at 5.2M should not be required for a 6 rad system, even CC1 at 4.2M is probably not required.
Suggest changing to CC1, (4.2M), if rads all still getting hot then suggest changing to CP1 which at a constant 3M should still be quite adequate, if everything still OK then give PP2 a go and see how you get on, leave the towel rad valves as is to act as a bypass. You may be OK on PP2 but unfortunately Grundfoss rarely seem to get these PP settings right, they are normally too low, a pity.

Whar vent and cold feed arrangement do you have?.

 

[ukmark62]

Thanks for getting back. I'll try CC1 first.

Does leaving the towel rad fully open act as a kind of expansion vessel then?

I think I did close the towel rad valve quite a lot a few days ago and that seemed to cause a lot of water up the vent pipe into the expansion tank. I then opened it back up and that does appear to help control the expansion. Am I right in saying that if the pump speed is too high it can also cause this expansion up the vent pipe (pressure too high??). And if pump speed is too low, the boiler overheats and that can also cause the expansion up the vent pipe?

The vent pipe comes out of the cold tank in the loft and raises high above the tank and then u-bend into expansion tank. I don't know if that answers your question. It's been unchanged for many years. Ballcock valve was replaced on expansion tank last year.

Thanks again.

 

[Johntheo5]

Thanks for getting back. I'll try CC1 first.

Does leaving the towel rad fully open act as a kind of expansion vessel then?

No, the F&E cistern is where the few litres of expansion go to on system heat up, the level in this cistern (and also in the vent pipe) will rise by ~ 10/15cm depending on the dimensions of the cistern.

I think I did close the towel rad valve quite a lot a few days ago and that seemed to cause a lot of water up the vent pipe into the expansion tank. I then opened it back up and that does appear to help control the expansion. Am I right in saying that if the pump speed is too high it can also cause this expansion up the vent pipe (pressure too high??). And if pump speed is too low, the boiler overheats and that can also cause the expansion up the vent pipe?

The pump head, if too high, or increases due to shutting off the towel rad, can cause pump over into the F&E cistern but this normally is a sympton of a incorrectly installed (or partially blocked) vent and cold feed, can you post a photo of your arrangement and also the area around and including the UPS3, have you got a 3 port mid position valve whereby you can select CH or HW or CH and HW.

The vent pipe comes out of the cold tank in the loft and raises high above the tank and then u-bend into expansion tank. I don't know if that answers your question. It's been unchanged for many years. Ballcock valve was replaced on expansion tank last year.

As above, can you post a photo. a extensively used vent and cold feed arrangement is where, with the pump pumping from the boiler flow pipe has, from the boiler and close to the pump, the vent, then the cold feed no more than 150mm from the vent and then the pump.
My 50 year old system has a combined vent&cold feed where pump over cannot occur, some rads are > 40 years old.

Thanks again.

 

[ukmark62]

Pic 1 - this is how I choose CH, HW or both. This panel lets me set timers etc for each. Don't know where the 3 port valve would be.
Pic 2 - upstairs in loft showing part of expansion tank - the wooden surrounds been there for years
Pic 3 - bottom part of expansion tank
Pic 4 - vent pipe coming out of cold tank into expansion tank
Pic 5 - cold feed coming from loft into airing cupboard. Cold tank is very close to expansion tank - maybe 6-8 inches apart from each other
Pic 6 - hot water cylinder in airing cupboard
Pic 7 - Grundfos pump just in front of hot water cylinder

 

[Johntheo5]

Not clear to me as yet, can you see or show where the pipe (called the cold feed) coming from the bottom of the F&E cistern joins the system, this is the pipe shown in pic.3, where does it tee into the system?, its also a ss flexible??.

 

[ukmark62]

The ss flexible pipe seems to go underneath the cold storage tank and then is out of sight. My best guess based on where it disappears is that it is connected to one of these pipes coming down from the loft directly below the cold storage tank. The 3 pics go from the top of the airing cupboard to the bottom.

The red wheel at the bottom is almost fully open. IIRC that has something to do with the hot water for upstairs tap in bathroom sink - but not sure. We have an electric mira shower.

I don't really mess with these things as everything's been working fine. We have the boiler serviced each year through a company called North West Heating Ltd. This system has been like this for at least 15 years (possibly longer). The Icos boiler was installed end of 2007.

BTW - so far on CC1, no overflowing and pump is very quiet. Thanks so much for your help.

 

[ukmark62]

No more water going up the vent pipe into the expansion tank. With CC1 as you advised AND leaving towel rad fully open, this is working 100%. No issues. I am still getting plumber round to look at installing ABV so that we can turn towel rad down. I will ask if he can see any partial blocks, but I think this is all down to us having TRVs installed on 6 rads last may when flush was done. When I start to close towel rad and all TRVs are closed, then there's nowhere for expanded water to go, so it goes up the pipe. Hope the ABV will fix it so we can close towel rad to a more comfortable setting. Thanks for your help.