Radiators not reaching flow temperature

[Helene]

Apologies in advance as I'm far from an expert - hence why I'm seeking advice!

We had a Mitsubishi Zubadan 14KW fitted in Oct 2023. It works really well in some rooms and others (definitely bigger and with higher heat loss) it's been challenging.

I don't think the system is well balanced as our loft K3 rad doesn't get much heat at all - so I'm hoping an engineer will come and help after all our failed attempts at balancing the system.

 

My question today is - if the heat pump flow temp is at 40 degrees - but I measure 33 degrees maximum on the hottest radiator's flow pipe.... shouldn't it get 40 degrees? (return pipe is around 23 degrees, but delta will depend on the radiators at the moment, I have as low at 2 degree delta on some radiators). Just wondering if some rooms struggle to heat up because the flow temp is too low to start with... 

 

Thank you

[sharpener]

1 hour ago, Helene said:

after all our failed attempts at balancing the system

 

What have you tried?

 

1 hour ago, Helene said:

It works really well in some rooms

 

A good approach is to gradually close the lockshield valves on the rads in the rooms that are getting up to temperature OK.

 

Measured with the same instrument you should get the same temp at the inlet to the rads as at outlet of the HP perhaps less a degree or two for losses down the pipework. More would indicate poor flow rate or very poor pipe insulation. Flow temp indicated on the HP display might be different.

[Gary68]

Do you have the Melcloud app so you can see the flow and return temperatures by hour?  If not, go to the service menu on the controller and go to thermistor readings and post a screenshot this is will till you the flow and return temp of the heat pump circuit.  Whilst you are there go into running information and type in 540 this will give you the flow rate of the heat pump in litres per minute.

 

If its not bad balancing of your rads and the heat pump is struggling to get up to the required temperature it could be due to low flow rate.

[ReedRichards]

9 hours ago, Helene said:

My question today is - if the heat pump flow temp is at 40 degrees - but I measure 33 degrees maximum on the hottest radiator's flow pipe.... shouldn't it get 40 degrees?

 

Not necessarily.  A lot of heat pump systems have a buffer tank to make sure there is always a sufficient volume of water.  In a 4-port buffer it's possible that there is some mixing between the water entering your heating system and the water returning from the radiators.  If that happens then the water that enters your heating system isn't as hot as the water that leaves your heat pump.  But I would not expect the difference to be as great as 7 degrees.  Is the flow temperature measured as 40 degrees or is that what it is supposed to be? 

[Helene]

6 hours ago, Gary68 said:

Do you have the Melcloud app so you can see the flow and return temperatures by hour?  If not, go to the service menu on the controller and go to thermistor readings and post a screenshot this is will till you the flow and return temp of the heat pump circuit.  Whilst you are there go into running information and type in 540 this will give you the flow rate of the heat pump in litres per minute.

 

If its not bad balancing of your rads and the heat pump is struggling to get up to the required temperature it could be due to low flow rate.

 

Hi Gary, I don't have the Melcloud yet (they're waiting for wifi controller to get back in stock) but I have been monitoring thermistor readings etc - and it always looks fairly healthy. Example on a cold day 43 degrees flow and 38 degrees return.

Since writing this post, I think I realised that loads of our radiators have the lockshield valve and TRV valves mixed up - so I managed to get some radiators to the actual flow temp - however the system is still not balanced as many radiators are cold (their flow pipe is hot but the return pipe is cold)... I am indeed starting to question the flow rate - how can this be addressed? The flow rate is around 32/33L ... how can I tell if it's good enough?

 

To add some context, it's a big 4 bedroom house with loft so we have many radiators - and it's very hard to tell the piping circuit, especially given the house has been extended. 

 

Thank you

[Helene]

7 minutes ago, ReedRichards said:

 

Not necessarily.  A lot of heat pump systems have a buffer tank to make sure there is always a sufficient volume of water.  In a 4-port buffer it's possible that there is some mixing between the water entering your heating system and the water returning from the radiators.  If that happens then the water that enters your heating system isn't as hot as the water that leaves your heat pump.  But I would not expect the difference to be as great as 7 degrees.  Is the flow temperature measured as 40 degrees or is that what it is supposed to be? 

The heat pump tells me that it's at 40 degrees (and it's what the curve is setup at for the relevant outside temperature)
However, since writing this post, I think I realised that loads of our radiators have the lockshield valve and TRV valves mixed up - so I managed to get some radiators to the actual flow temp - however the system is still not balanced as many radiators are cold (their flow pipe is hot but the return pipe is cold)

[Helene]

8 hours ago, sharpener said:

 

What have you tried?

 

 

A good approach is to gradually close the lockshield valves on the rads in the rooms that are getting up to temperature OK.

 

Measured with the same instrument you should get the same temp at the inlet to the rads as at outlet of the HP perhaps less a degree or two for losses down the pipework. More would indicate poor flow rate or very poor pipe insulation. Flow temp indicated on the HP display might be different.

 

I have tried the following methods:
- Turning the lockshield valve off gradually for the radiators getting hotter quicker - but it's proven really hard because the house is big, the circuit might be all over the place (due to house extension) and various radiator types (most are K2/K3 but a few a single convector or towel rails, the latter being the hardest in my opinion, and can strangely have a big impact)

- Using thermometers to try to get a delta to 5-7 degrees - only realised that a lot of our lockshield valves and TRVs have been mixed up so I'm having to re-do it all, however with 16 radiators it feels like I'm going nowhere... 
it seems that doing that gave me 10 degrees different on the flow pipes of different radiators... so far from the 1-2 degrees difference.

 

Thank you
 

[HughF]

Modern lockshield valves are mostly junk, with a lot of the action happening in the last 1/2 turn.

 

i tried and failed to get my system balanced too, and my k3 is always a bit cooler on the outside panel than on the inside. 
 

in the end i just wound them all wide open and jumpered the call for heat line with a wago connector. It runs 24/7 on weather compensation.

[ReedRichards]

Surely with weather compensation you absolutely need all your radiators balanced, @HughF?  Otherwise some rooms are permanently too hot and others permanently too cold?  If your radiators have TRVs you're not supposed to use them with weather compensation,  certainly not the "hard core" weather compensation that the likes of Heat Geeks would advocate.  Or do you leave all the doors open and have fans to distribute the air around your dwelling?  

[HughF]

We leave all the doors wide open…. Trvs in the bedrooms stop them getting too hot.

 

Although in the downstairs, there’s no such thing as too hot for my wife. She’s quite happy if it’s anywhere between 22-25.

 

It seems to work out quite ok for us. The troublesome northern room sits at 21.5 ish in these climatic conditions, and the rear of the house (with a new build extension to regs+) sits at 22 ish.

 

I think it helped that I got the rad sizing pretty much bang on and I’ve only for one rad per drop off a 22mm ring.

 

We actually only have two rads downstairs. The hall and kitchen are served by fan coils and the extension is ufh.

Edited January 18 by HughF

[Gary68]

10 hours ago, Helene said:

 

Hi Gary, I don't have the Melcloud yet (they're waiting for wifi controller to get back in stock) but I have been monitoring thermistor readings etc - and it always looks fairly healthy. Example on a cold day 43 degrees flow and 38 degrees return.

Since writing this post, I think I realised that loads of our radiators have the lockshield valve and TRV valves mixed up - so I managed to get some radiators to the actual flow temp - however the system is still not balanced as many radiators are cold (their flow pipe is hot but the return pipe is cold)... I am indeed starting to question the flow rate - how can this be addressed? The flow rate is around 32/33L ... how can I tell if it's good enough?

 

To add some context, it's a big 4 bedroom house with loft so we have many radiators - and it's very hard to tell the piping circuit, especially given the house has been extended. 

 

Thank you

 

From the figures you have posted the heat pump is working fine you have a good DT of 5 and the flow rate is more than adequate, it does sound like its simply down to the flow through the radiators which should be easily remedied.  Good luck

[Helene]

3 hours ago, HughF said:

Modern lockshield valves are mostly junk, with a lot of the action happening in the last 1/2 turn.

 

i tried and failed to get my system balanced too, and my k3 is always a bit cooler on the outside panel than on the inside. 
 

in the end i just wound them all wide open and jumpered the call for heat line with a wago connector. It runs 24/7 on weather compensation.

It's good to know for the K3 as I always feel like it's not getting hot enough, or not entirely filled up.  What does the wago connector do? Thanks

[PhilT]

3 hours ago, Helene said:

It's good to know for the K3 as I always feel like it's not getting hot enough, or not entirely filled up

have you tried bleeding the K3 in the loft?

[sharpener]

9 hours ago, HughF said:

Modern lockshield valves are mostly junk, with a lot of the action happening in the last 1/2 turn...
 

in the end i just wound them all wide open and jumpered the call for heat line with a wago connector. It runs 24/7 on weather compensation.

 

5 hours ago, Helene said:

 What does the wago connector do? Thanks

 

It bypasses the connection from any thermostats and make the HP run the entire time.

[Helene]

7 hours ago, PhilT said:

have you tried bleeding the K3 in the loft?

We did but bleeding it (although needed) didn't help - I think I'm starting to make progress now that I've identified which sides are flow pipes and return pipes... didn't help that I knew nothing about anything to start with and that the new rads were fitted the wrong way around. 

[HughF]

10 hours ago, Helene said:

We did but bleeding it (although needed) didn't help - I think I'm starting to make progress now that I've identified which sides are flow pipes and return pipes... didn't help that I knew nothing about anything to start with and that the new rads were fitted the wrong way around. 

There isn’t a ‘wrong way round’ for lockshields and TRVs (although logically, my head still tells me the trv should be on the flow), but if your rads are plumbed TBOE then it’s important than the flow is to the top, otherwise the rads will be short circuited.

[PhilT]

11 hours ago, Helene said:

We did but bleeding it (although needed) didn't help - I think I'm starting to make progress now that I've identified which sides are flow pipes and return pipes... didn't help that I knew nothing about anything to start with and that the new rads were fitted the wrong way around. 

Does the K3/loft air temp now meet your requirements?

[Helene]

1 hour ago, PhilT said:

Does the K3/loft air temp now meet your requirements?

Thanks for asking, still not - it's getting slightly warmer but cold return flow... it feels like all the working rads are on the edge of (hot/completely cold) if I turn them down in the slightest so I wonder if it will even get balanced.

[PhilT]

2 hours ago, Helene said:

Thanks for asking, still not - it's getting slightly warmer but cold return flow... it feels like all the working rads are on the edge of (hot/completely cold) if I turn them down in the slightest so I wonder if it will even get balanced.

I had a similar issue on commissioning. I have a huge K3 in my conservatory and it's the furthest location from the source. I ran my system day and night for over a week, with all rad valves fully open, until temperatures reached a steady state within the spec ball park, which they did. So I would persevere, running 24/7 with all rad valves 100% open, then after a week if it's still not balanced you can start tweaking and/or considering other remedies.

Edited January 19 by PhilT

[Helene]

6 minutes ago, PhilT said:

I had a similar issue on commissioning. I have a huge K3 in my conservatory and it's the furthest location from the source. I ran my system day and night for over a week, with all rad valves fully open, until temperatures reached a steady state within the spec ball park, which they did. So I would persevere, running 24/7 with all rad valves 100% open, then after a week if it's still not balanced you can start tweaking and/or considering other remedies.

It's been nearly 3 months

I was leaving with it until the cold came back.
So you didn't have to do anything and it balanced itself?

[PhilT]

21 minutes ago, Helene said:

It's been nearly 3 months

I was leaving with it until the cold came back.
So you didn't have to do anything and it balanced itself?

yes - my rad and room temps were all over the place to start with, I think partly due to the glycol antifreeze gradually working its way through the system, and partly due to my microbore system, so I deliberately ran it hotter than needed continuously for as long as possible to resolve those issues. If you can't get it to work by running hot continously 24/7 with all rad valves open then (statement of the bleedin' obvious) you have other issues that need an expert inspection.

[SimonD]

Assuming that your heatpump is outputting 14kW, if it's at a Delta T of 5C - eg flow 40/35 or flow 45/40 - this should equate to a flow rate of around 40l/min. 30-33l/min equates to an output of 11-12kW at 5C Delta T

 

With regard to your radiators, you need to be more methodical:

 

- let the system go completely cold and then turn the heating on - as it warms up check and make note of the order in which the radiators get warm and then take note of the temperature of each radiator when the system has been running for a good period of time.

 

- To easily see if you can get hot water to the coldest rad, simply turn off the hottest radiators using the TRV only and then see if heat gets pushed to that cold radiator.

 

 

[Helene]

1 hour ago, SimonD said:

Assuming that your heatpump is outputting 14kW, if it's at a Delta T of 5C - eg flow 40/35 or flow 45/40 - this should equate to a flow rate of around 40l/min. 30-33l/min equates to an output of 11-12kW at 5C Delta T

 

Thanks so what would be the reason to have a lower flow? wrong balancing?

 

1 hour ago, SimonD said:

 

With regard to your radiators, you need to be more methodical:

 

- let the system go completely cold and then turn the heating on - as it warms up check and make note of the order in which the radiators get warm and then take note of the temperature of each radiator when the system has been running for a good period of time.

The former is hard as it's a big house and I think the circuits splits in various places, and I don't know where... and there are various radiator types... but worth trying again.

 

1 hour ago, SimonD said:

 

- To easily see if you can get hot water to the coldest rad, simply turn off the hottest radiators using the TRV only and then see if heat gets pushed to that cold radiator.

 

 

I've done that at the beginning and coldest radiators worked perfectly well - just not when all the rads went back on.

[Helene]

2 hours ago, PhilT said:

yes - my rad and room temps were all over the place to start with, I think partly due to the glycol antifreeze gradually working its way through the system, and partly due to my microbore system, so I deliberately ran it hotter than needed continuously for as long as possible to resolve those issues. If you can't get it to work by running hot continously 24/7 with all rad valves open then (statement of the bleedin' obvious) you have other issues that need an expert inspection.

I could give it a shot when temps get higher again... as it would cost a lot at the moment 😬

[PhilT]

47 minutes ago, Helene said:

I could give it a shot when temps get higher again... as it would cost a lot at the moment 😬

SimonD suggested a 40l/min flow rate, so 33l/min, although very high compared to mine, may not be enough to shove water all the way around your big house and up into your loft K3! Do you have one or two flow pumps? if you have only one either it's not man enough or it is not set to a high enough speed. If you have two, check the other (secondary flow to rads) pump and increase its speed or, if not already, try setting to maximum speed. This should be quite easy as long as you can get access to both. Usually they have 3 speeds which can be adjusted via a dial or a button which selects 1, 2 or 3 lit LED's. You should be able to hear the speed increase.