New boiler, last rad heats up then goes cold

FataVerde

I had a Viessmann boiler installed this August in a one-bedroom flat with 5 rads (4 upstairs, 1 ground floor entrance). The gas engineer was supposed to do a chemical flush but not sure how thorough it was. Then he was meant to balance the system, which took him two minutes and the last rad in the system was very slow to warm up. The rest heated up quickly, including the rad just next to this one in the living room. Since starting to use the heating in Oct, I noticed this last rad sometimes would heat up, but then immediately goes cold and the first rad in the living room does all the heavy lifting (it's burning hot) to get the room temp to the one I set via the Nest thermostat. Both rads are set at 5 on the valve. The Viessmann boiler is connected via OpenTherm to my Nest and that's how I control the temperature. Any ideas what could be the problem? Could there be some settings in my Nest? Or piping work? I have the very thin copper pipes. Or anything else? 

Mutton_Geoff

Balancing CH systems takes longer than 2 mins. Took me half a day to do a 4 bed house.

A quick search will reveal the tips and tricks.

ThisIsWeird

Hi FV.

You have the Nest in the sitting room? And the rads in that room have TRVs on them? Ideally they shouldn't, but as long as they are set to '5' - which is an equivalent temp that's very unlikely to be reached - it should be fine.

First thing I'd suggest trying, tho' - with the TRV head on '5', unscrew it by undoing chrome knurled ring immediately under it, and fully remove the head. Does it now heat up?

Press the exposed pin down - it'll be firm, so use a blunt object to save your thumb. Does it move smoothly, bottom-out with a firm 'thunk', and jump back up when released?

Ok, if the pin does move smoothly, then leave the head off, and pull off the cap on the valve on other side. This may need a screw removed from the cap, but is usually pull-off. This valve is the 'lockshield'. Get a wee piece of paper and some sellotape, and stick a 'flag' on the spindle pointing into the room. This is so you can always return that spindle to the same position. Now first turn that spindle clockwise unti it stops - the valve will be fully closed. Note down how many turns and part-turns this takes - and let us know.

Now return that spindle to its starting position, and give it one half-turn more open (anti-clockwise). Any difference?

Finally check the fitted magnetic filter to see if it's collected any sludge. Let us know. (post a photo.)

FreeBear

FataVerde said:

I had a Viessmann boiler installed this August in a one-bedroom flat with 5 rads (4 upstairs, 1 ground floor entrance). The gas engineer was supposed to do a chemical flush but not sure how thorough it was. Then he was meant to balance the system, which took him two minutes and the last rad in the system was very slow to warm up. The rest heated up quickly, including the rad just next to this one in the living room.

If my memory serves correctly, this boiler was a drop in replacement for an Ideal Logic combi - Assuming the old setup was working, there shouldn't have been any need to fiddle with the radiators on fitting the 050-W boiler.

If the engineer has messed up the balance, I'm afraid you are going to have to do it yourself (unlikely you'll get him back without paying quite a bit of money). That said, you might get Heatable to send someone out free of charge if you can persuade them that the original engineer made a mess of the job.

ThisIsWeird

I wonder if, with chemical cleans - or even powerflushes - the installers 'temporarily' opened up the lockshields to get a good flow through? They'd surely have to?
And then closed them back off in a crude manner.

400ixl

Sounds like the system is not balanced properly. Best to research on how to do it yourself and start completely from scratch.

Mutton_Geoff

A quick note for wannabee rad balancers, my experience has been that most of the rads have the lockshield only half to one turn from fully closed to set them correctly whilst only one or two (at the far end of pipe runs usually) are half way or fully open.

FataVerde

ThisIsWeird said:

Hi FV.

You have the Nest in the sitting room? And the rads in that room have TRVs on them? Ideally they shouldn't, but as long as they are set to '5' - which is an equivalent temp that's very unlikely to be reached - it should be fine.

First thing I'd suggest trying, tho' - with the TRV head on '5', unscrew it by undoing chrome knurled ring immediately under it, and fully remove the head. Does it now heat up?

Press the exposed pin down - it'll be firm, so use a blunt object to save your thumb. Does it move smoothly, bottom-out with a firm 'thunk', and jump back up when released?

Sorry, I could only get to this over the weekend. Thanks so much! This worked, i.e. the rad heated up when I removed the TRV head. Heatable was actually quite nice and ready to send the gas engineer back, but glad this worked. I suspect the spring in the head is not working. I bought my two rads from Screwfix and they came with this pair of valves - Kudox TRV & L/S 15mm - on discount, which seem very flimsy. My question is: Can I replace the broken valve head with another brand fitting 15mm. I couldn't find this same Kudox brand and I'm not sure I want to replace it with the same bad valve. I found a Drayton RT414 (15mm) at a good price, but would that fit? I plan to use the TRVs to turn off rads when I don't want the heat on in that room. I kind of carry the thermostat with me to whatever room I need heated in the house.

FataVerde

FreeBear said:

FataVerde said:

I had a Viessmann boiler installed this August in a one-bedroom flat with 5 rads (4 upstairs, 1 ground floor entrance). The gas engineer was supposed to do a chemical flush but not sure how thorough it was. Then he was meant to balance the system, which took him two minutes and the last rad in the system was very slow to warm up. The rest heated up quickly, including the rad just next to this one in the living room.

If my memory serves correctly, this boiler was a drop in replacement for an Ideal Logic combi - Assuming the old setup was working, there shouldn't have been any need to fiddle with the radiators on fitting the 050-W boiler.

If the engineer has messed up the balance, I'm afraid you are going to have to do it yourself (unlikely you'll get him back without paying quite a bit of money). That said, you might get Heatable to send someone out free of charge if you can persuade them that the original engineer made a mess of the job.

Yes, that's right. The only issue is that I don't know if the rad had worked with the previous boiler as I rented the place last winter, when I was out of London, and the rads had just been installed a few months before when it was nice and warm. I imagine the tenant at the time would have told me if he had any issues with the rad, but maybe it broke when he barely needed it, who knows? Heatable was convinced it's an issue with the rad, but they offered to send the engineer back. Thankfully, thanks to a suggestion above, I got this figured before they had to come back. Heatable sent them back to change the position of the boiler (there was not enough clearance even though this was like for like, but Viessmann has different requirements) so the poor guy came back for this and then again to change the position of the heatlink, which had stopped linking to my nest when he changed it with the boiler. 

FreeBear

FataVerde said:  I bought my two rads from Screwfix and they came with this pair of valves - Kudox TRV & L/S 15mm - on discount, which seem very flimsy. My question is: Can I replace the broken valve head with another brand fitting 15mm. I couldn't find this same Kudox brand and I'm not sure I want to replace it with the same bad valve. I found a Drayton RT414 (15mm) at a good price, but would that fit?

There are (I think) two different size threads used for TRV heads. 28mm and 30mm. The pins are sometimes different lengths too. The Drayton valve has a 30mm thread, and the pin protrudes 9.32mm from the body.

ThisIsWeird

FataVerde said:

ThisIsWeird said:

Hi FV.

You have the Nest in the sitting room? And the rads in that room have TRVs on them? Ideally they shouldn't, but as long as they are set to '5' - which is an equivalent temp that's very unlikely to be reached - it should be fine.

First thing I'd suggest trying, tho' - with the TRV head on '5', unscrew it by undoing chrome knurled ring immediately under it, and fully remove the head. Does it now heat up?

Press the exposed pin down - it'll be firm, so use a blunt object to save your thumb. Does it move smoothly, bottom-out with a firm 'thunk', and jump back up when released?

Sorry, I could only get to this over the weekend. Thanks so much! This worked, i.e. the rad heated up when I removed the TRV head. Heatable was actually quite nice and ready to send the gas engineer back, but glad this worked. I suspect the spring in the head is not working. I bought my two rads from Screwfix and they came with this pair of valves - Kudox TRV & L/S 15mm - on discount, which seem very flimsy. My question is: Can I replace the broken valve head with another brand fitting 15mm. I couldn't find this same Kudox brand and I'm not sure I want to replace it with the same bad valve. I found a Drayton RT414 (15mm) at a good price, but would that fit? I plan to use the TRVs to turn off rads when I don't want the heat on in that room. I kind of carry the thermostat with me to whatever room I need heated in the house.

Pleased that worked. 
TRV heads can fail with the activating 'plunger' in the heads being permanently extended, so the valve will be turned off whenever the head is in position - seems to be what happened here. They usually last a good decade at least, tho'.
Sorry, no idea which other makes will fit. What makes of TRV do you have in other rooms? If different, you could always try. Or, the required info will be 'out there' on t'web!
If you often turn the rads in this room off, and move the Nest controller around, would you consider splashing out on a Smart Nest TRV? I have a Hive, with one Smart on the bedroom rad - it then comes on an hour before bed, and an hour at wake-up - saves the stupid hassle of having to manually operate that rad, or having it wastefully running when not needed.
EDIT: are they available for Nest?!