CH with Microbore bypass loops and proper bypass valve

[Rob1234]

Hi - and thanks in advance for reading - just joined...

I have been looking into why my heating takes ages to warm up - had the system power flushed and lots of things checked... Today, I found this:

This is one of 4 manifold pairs - and it also feeds the worst of the radiators for not warming up.. Is it correct or normal to have the two loops from flow to return like this?

The bypass loops are (predictably) lovely and (ouch) hot - the feed to the rad gets hot-ish after a while and the return from the rad barely warms up at all, this is with the stop valve on the rad open and the TRV removed. The radiator has ben taken off and flushed out with a hose as well.

Is this in any way normal practice? Can I fit 4 blanking plugs and rely on the bypass pressure relief valve? - It is marked from 0.1 to 0.5 bar, any good starting point for settings would be appreciated!

FYI, 15 rads in all on Viessmann 100-W 19KW boiler, house built 2002

Thanks for reading - any ideas and info much appreciated

 

[John.g]

What setting is the ABV (bypass) set to now and where is it located?, ie close to the boiler or at the other end.
When the rads are cold, and after the boiler fires up, just shut that by pass (setting 0.5) and see do the flow&return pipes heat up faster/better. Also ensure the ABV piping goes cool/cold, it may be leaking past.
When the ABV outlet pipe cools down, very slowly reduce the setting until you just feel the pipe getting warm (this may happen at ~ 0.3 to 0.4 setting) and then turn the adjusting knob back (clockwise?) down by approx a 1/4 to 1/2 a turn, this should reclose the ABV which will/should reopen when TRVs, if fitted, close in, or zones shut off or the boiler shuts down, You will have to tune this over a period but should get it reasonably right after a while. Unfortunately, quite a lot of circulating pumps now operate in a mode that makes it difficult to get a proper setting.

 

[Rob1234]

Hi John, thanks for the quick reply - Boiler is in garage, quite a way from the ABV in airing cupboard near the 2 zone valves (water and CH)

Any thoughts on the bypass loops in the photo?

 

[John.g]

No, I have never seen this type of manifold, presume these by pass loops are separate from the ABV which is normally installed between the (main) flow & return piping so don't know what these others are for except that the ABV has control?, if it has then they will get cool when its shut.

 

[Rob1234]

These bypass loop are always hot if the boiler is running - they are directly between the feed and return and obviously a much easier route for the water than going round the much longer microbore to the rads as well as rads and TRVs along the way...

 

[ShaunCorbs]

Need to remove them loops / short circuits

 

[Rob1234]

Hi Shaun - Thanks for that, I was looking for some reassurance that they are not needed - or just plain wrong... They have been in place since the house was built, I would say - I had to make a new access hole in the floor to get to them...

When I moved in, it was a Y-plan setup and there was a simple gate valve as another bypass, I had it changed to S-Plan with an ABV.

Thanks for the info on New year - and a Saturday as well - now I just need to find the blanking plugs on a bank holiday weekend...

Anyone around Coventry who I can cross your palm, please shout

 

[ShaunCorbs]

Screwfix

Worst comes to the worst 10mm push fit cap ends and inserts

 

[John.g]

Hi Shaun - Thanks for that, I was looking for some reassurance that they are not needed - or just plain wrong... They have been in place since the house was built, I would say - I had to make a new access hole in the floor to get to them...

When I moved in, it was a Y-plan setup and there was a simple gate valve as another bypass, I had it changed to S-Plan with an ABV.

Thanks for the info on New year - and a Saturday as well - now I just need to find the blanking plugs on a bank holiday weekend...

Anyone around Coventry who I can cross your palm, please shout

Would like to know the rationale behind those uncontrolled bypasses.

Would also suggest installing a 22mm gate/lever valve in series with the ABV as you will achieve more control due to the circ pump mode, you could consider doing it in conjunction with the above as your system will be drained/partially drained down anyhow.

 

[Rob1234]

Would like to know the rationale behind those uncontrolled bypasses.

Would also suggest installing a 22mm gate/lever valve in series with the ABV as you will achieve more control due to the circ pump mode, you could consider doing it in conjunction with the above as your system will be drained/partially drained down anyhow.

Hi John, thanks for that - that is exactly what I have actually got now - there was a ABV that was letting some water through all the time, regardless of setting - so I got it changed and a gate valve added...

When I moved in, there were two bypass radiators (no trv), a simple gate valve for bypass and those two loops in the photo... I think someone was not really understanding how it should work...

Mind you - there were fluorescent lights under the kitchen cupboards behind wooden plinth strips as well...

I know you don't believe me so here you go:

And yes, they were wired and working when the lights under the top cupboards were turned on...

 

[John.g]

What make of ABV is installed now?.

 

[Rob1234]

Not sure what make it is...
But - stop ends fitted and I now have 20-25C drop on the return - It was 10-12C before BUT the boiler is sitting at 26% modulation with 72C flow, 51C return and still not getting much flow it seems...

Thanks for help and advice everyone and kudos for screwfix being open today - I think I need to start a new appropriate topic for the boiler!

 

[Rob1234]

Screwfix

Worst comes to the worst 10mm push fit cap ends and inserts

Thanks Shaun - Screwfix were open today, it was not apparent from their web site - and yes, push fit caps and inserts was the way to go, I figured not messing with the 19 year old manifold connections was preferable...

 

[John.g]

Not sure what make it is...
But - stop ends fitted and I now have 20-25C drop on the return - It was 10-12C before BUT the boiler is sitting at 26% modulation with 72C flow, 51C return and still not getting much flow it seems...

Thanks for help and advice everyone and kudos for screwfix being open today - I think I need to start a new appropriate topic for the boiler!

If the boiler is at 26% output then only running at 4.94kw and a flowrate of 3.37LPM!! If that is correct then something seriously amiss. Is the DHW cylinder heat up time OK.

 

[ShaunCorbs]

10mm gets blocked very easily sounds like you need to start looking at maybe a blockage at the inserts

 

[Rob1234]

If the boiler is at 26% output then only running at 4.94kw and a flowrate of 3.37LPM!! If that is correct then something seriously amiss. Is the DHW cylinder heat up time OK.

Yes - Cyl seems to heat up fine - all 22mm between boiler and cyl, predictably...

It's got sludge removing stuff in the system at the moment, which is still building up on the filter magnet to maybe 2 - 3 mm thick bumps in a day or 2, - I'm hoping this starts to clear more out now the flow is going round the rads instead of the bypass loop stupidity...

Before the boiler change, I had a grundfos pump set at maximum rate and that did heat up the rads OK (old glowworm 18HXi, looked ready to die at any moment)

Th new Vitodens has a more powerful pump internally - but the boiler never seems to set it above 65% speed, making it less powerful than my old one - and there's no minimum speed setting option, only a max speed setting for the pump, which I had already set to 100% before I found the bypass loops... The boiler pump is a fancy PWM controlled version, so no switch or buttons to play with, unfortunately.

I was wondering about getting the old pump put back in place...

 

[Rob1234]

10mm gets blocked very easily sounds like you need to start looking at maybe a blockage at the inserts

Hi Shaun, yes, the plumbers who fitted the boiler really don't like the push-fit and I can see why, having seen the little holes in the inserts... Unfortunately cheapskate Persimmons pay installers by the number of houses they complete, so quick and dirty is very much what you get. I was really hopeful that blanking off the loops was going to fix it all, but still some work required it seems... I'll keep the system pumping through the worst rad in the daytime for another couple of days and see how much more gritty gunk comes out I think..

Thanks for your help and suggestions - Screwfix today was a real bonus

 

[ShaunCorbs]

The boiler controls the pump to manage a difference of 20dc flow and return

 

[ShaunCorbs]

Hi Shaun, yes, the plumbers who fitted the boiler really don't like the push-fit and I can see why, having seen the little holes in the inserts... Unfortunately cheapskate Persimmons pay installers by the number of houses they complete, so quick and dirty is very much what you get. I was really hopeful that blanking off the loops was going to fix it all, but still some work required it seems... I'll keep the system pumping through the worst rad in the daytime for another couple of days and see how much more gritty gunk comes out I think..

Thanks for your help and suggestions - Screwfix today was a real bonus

They will be straight runs so worse comes to worst remove from the manifold clean the inserts if blocked and do the same at the rads and all should be good

Easy way to spot them if any rad is very slow to heat / doesn’t

 

[Rob1234]

They will be straight runs so worse comes to worst remove from the manifold clean the inserts if blocked and do the same at the rads and all should be good

Easy way to spot them if any rad is very slow to heat / doesn’t

The boiler only goes to 60% even with 30C drop when I put more rads on - I feels like it's trying to be too efficient and if there was more flow, the boiler could ramp up more, like the old one did.

The pipe run to the worst rad is far from straight or sensible, the rads all have a pair of elbows on each pipe at the hole in the plasterboard and swap to copper microbore from the hole to the rad itself, so loads of opportunities for blockages, but the flow at the valves when the rads were off for hosing through seemed pretty strong.

 

[John.g]

If your pump is now limited to 65% then its only a 3M pump, if it ran at full speed (6.8M) then you should get ~ 5.1LPM, still pretty hopeless, did you just hose through the rads individually or/and did you hose through the system with the manifolds and rads connected up?. Unlikely the problem but you might remove the TRV actuators from 3 or 4 rads and ensure the valve pins are fully out.
Have you a sealed system?., if so, and if you have a boiler pressure gauge note how much it rises (or falls) when you start the boiler/circ pump, if the pump is producing a 3M head then the boiler PG should rise by 0.3bar.

Even with a dT of 30C and assuming you have 18kw of installed rads then the boiler should still output ~ 12.7kw (67%). though 30C dT might be controlling the max boiler output.

 

[Rob1234]

It's a long story, but the system was power flushed before the new boiler was fitted - but now we know about the loops, so the flushing was most likely not as effective as it should have been, the large twin filters had a huge amount of build up on them twice, and the old boiler worked really well after the flushing, over night... New boiler fitted next day and converted to sealed and pressurised system, pump, tank and auto air vent all removed, ABV replaced a little later when we noticed it was stuck open a tiny bit, the three worst rads were taken off and flushed out with a hose - lots more black water from each of them...

The old boiler / pump was warming up the rooms pretty quickly - but now I get about 2 - 3C/hour temp rise like this, before today:

(Ignore the top line for the office - it's generally toasty in there!)

I have been removing the TRVs for testing and keeping the radiator with flow to try and flush it out more, hopefully they will improve move now the loops are not taking the flow away from the rads...

The temp rise before on the old boiler was far far steeper on the graphs...

 

[John.g]

Are you reasonably happy that there's no build up in your new boiler HX?, is the magnetic filter just that? or does it also collect sludge/dirt particles.
The boiler dT when heating the HW cylinder might tell you something if you take a few readings with cylinder temp ~ 50C and also before cut out at its setpoint, normally 60/65C.

 

[Rob1234]

Are you reasonably happy that there's no build up in your new boiler HX?, is the magnetic filter just that? or does it also collect sludge/dirt particles.
The boiler dT when heating the HW cylinder might tell you something if you take a few readings with cylinder temp ~ 50C and also before cut out at its setpoint, normally 60/65C.

Well the water heating works well, it seems - the filter is a MagnaClean Professional2, I'll see what it looks like a bit later after a day without the loops in place..

When they did the power flush, this is what the filters looked like twice:

It looked pretty bad to me - but I have no experience of what to expect...

 

[John.g]

I have no experience of these either, anyway next time the cylinder is heating on its own jot down the boiler flow&return temps.

 

[Rob1234]

I have no experience of these either, anyway next time the cylinder is heating on its own jot down the boiler flow&return temps.

When it was heating up this morning, I had 26C drop consistently as it heated up

 

[John.g]

That's a big dT with a cool/cold cylinder, would have expected less except there is a throttled in balancing gate valve on the coil return, there's none on mine and my dT starts at 8/10c when cold and just before cylinder cut out ~ 5/7C. I have a smart circ pump and its power output translates to a coil flowrate of ~ 12LPM which is confirmed by my 20kw oil fired boiler cycling times.. I'm just wondering if it's possibly a pump problem or some boiler protection (high dT) that's causing the high dT on CH as well. If you boiler % output is noted at the same time then the circ rate is easily calculatd but doesn't fix your problem.

 

[Rob1234]

Just a follow up for completeness...
I spoke to Viessmann tech support again and they suggested an engineer coming out to look at the boiler under warranty..

After some investigation, he was able to change the maximum pump speed from the 65% default limit on the 19kW boiler to 100% as per the 32kW model - and I now have radiators that are too hot to touch and much better warm up time in the house...

The setting was accessed via the Viessmann service assistant program on his laptop - but it may be possible to remotely configure the setting, he thought. It is not possible to change the setting from the boiler control panel.

He said it was unusual to need to do this, but the boiler control of the pump is geared towards it being eco-friendly and using the minimal amount of power required as per EEC regs - but clearly the pipe work here needed a far higher pump setting.

Thanks everyone for your help and advice with this