Impossible to fix flow problem? 4 grand down so far...

[Darryl Pullen]

Phoned Viessman today and they were adamant that is was a circulation problem (as am I). They even finished my sentence for me, I said "my boiler starts up, the temp increases... " and he said, "and then cuts-out at 50 degress, and goes back down again"... Apparently because it is looking for a temperature difference of 20 degrees between flow and return (as expected).

Best - I had thought that perhaps it could be some of the old piping right next to the boiler where the 3 returns join together, might explain why probalem seems to occur on HW only, HW and DH, and just CH?! Even though they are separate returns...

 

[sammathias]

Send us some pictures of this pipework fella.

 

[Rob Foster]

I like this type of problem, where are U based

 

[ShaunCorbs]

I like this type of problem, where are U based

about 80 miles between you and the op

 

[fixitflav]

Does it not sound normal to have 3 returns converging at the boiler, one comes up out of the screed, and two from upstairs.

There's nothing wrong with that, I've lived in houses with that arrangement. The only thing you need to watch is that all heating returns must be commoned before the HW return comes in, or you can get flow through rads when HW only calling. But it wouldn't cause your symptoms.
For your problem, do you have a 3-port valve or 2 (or more 2-ports)? If the latter, worth making sure none is stuck closed. Though if it's wired correctly the boiler and pump should run only when 1 or more is open, to avoided dead-heading.
Is there a bypass in the system? If that is wide open it might be taking all the flow, with little or none left for the rads.

 

[Rob Foster]

about 80 miles between you and the op

160 miles No bother thats about 2.5 gall of diesel in my stink pot 4 round trip, msg me and I will come and see what can be done.

 

[Darryl Pullen]

Got a three port valve, that is also new (well, 20 months old and seems to be working fine), it sits 2 inches above the pump. No idea if I have a bypass valve? Sorry, wouldn't know where to look?!

I turned all rads off apart from one earlier, and still no joy. The boiler simply shoots up to 50 then cuts-out, the rad does get a little heat into and would get hot if the boiler would stay on. Also, then turned on a towel rad, same story, rad immediately got warm, but never hot as the boiler wouldn't stay heating... So clearly, the circulation is not good, although the boiler is looking for 20 deg differential between flow and return rather than measuring flow rate I think.

So, it was sort of working, with around 8 rad (some turned off) at the end of winter, slow to heat, but would heat up eventually. And yet now, after being left for 4 months, doesn;t work at all. Not sure what that tells me!

 

[sammathias]

Don't the vitodens have an internal pump and you also have an external pump? Bypass would be fitted after pump before 3 port valve. Need some pictures of your set up...boiler pipework/ pumps etc.

 

[Jim Goodenough]

Have you checked pump valves are both fully open. Very basic suggestion but could be a knackered pump valve??

 

[fixitflav]

No idea if I have a bypass valve? Sorry, wouldn't know where to look?!

The bypass (if there is one) would be from pump discharge to boiler return, in parallel with the load, so if the rad controls throttle down to nothing there is still a flow through the boiler. I believe modern bypass valves don't just throttle but have some flow control feature, so they don't bypass a lot of flow when not necessary.

the boiler is looking for 20 deg differential between flow and return rather than measuring flow rate I think.

I don't understand that, perhaps the experts here can explain. For a given pump flow and boiler design output, the differential is fixed. If that is greater than 20°C, and the boiler is looking for a maximum 20° differential, when that is reached I would expect it to modulate (on a modern boiler) to maintain 20°, but then boiler output is below design. To get design output, need to increase the water flow. As the system heats up, if it's working properly the flow and return temperatures both rise, keeping the 20° differential.
But I don't see any advantage over controlling to a boiler flow (output) temperature, the more traditional way.
There doesn't seem any reason to think your water flow is blocked, and it would have to be severe to give your symptoms, so it looks to me like a boiler control issue. Might be worth discussing with Viessmann, and asking if there are any other options for boiler control.

 

[sammathias]

The boiler always "kettles" on starting up too.

Boiler empty

 

[Darryl Pullen]

Fixitflav - and that is what I don't get... Seems to me like perhaps I do have a circulation problem a bit but def no blockage as such. And it feels like the boiler is just too picky about the conditions it will operate in. Thinking the only way to tell for sure is putting a flow sensor in, on the return by the boiler? Could just be that I have some circulation, but very limited, the pipes are 35 years old...

 

[Darryl Pullen]

I also think if I was to put a huge pump in there, it might just work!

 

[fixitflav]

Fixitflav - and that is what I don't get... Seems to me like perhaps I do have a circulation problem a bit but def no blockage as such. And it feels like the boiler is just too picky about the conditions it will operate in. Thinking the only way to tell for sure is putting a flow sensor in, on the return by the boiler? Could just be that I have some circulation, but very limited, the pipes are 35 years old...

Maybe sammathias has a point, it could be as simple as that. What is system pressure? Is there flow from a vent point on the boiler, or the pipework close by?
Where is the expansion vessel connected?
Some photos and sketches would be useful.

 

[Darryl Pullen]

System pressure is sat around 0.6 bar rising up a bit when hot water is on currently. Can top it up later, didn't think that would make a huge difference? Expansion vessel is connected on the return I think, next to the boiler, will draw it out later... Wasn't sure I understood the question about flow from the vent point on the boiler?

 

[Harvest Fields]

Pressure should be between 1 and 1.5 dependant on boiler when cold

 

[Darryl Pullen]

I am thinking the only way to bottom this out is to buy some flow meters and determine once and for all if I have flow or note? One was suggested in earlier post, but also found these Piusi K24 AdBlue™ Flow Meter | BEST Price | In Stock | Fast Del|

 

[sammathias]

A small grundfos 15/50 will be capable of heating a 12 rad system...what makes you think a huge pump is going to make any difference? Going down the route of flow meters is just wasting time and money.
Time to get a decent heating engineer out and get him to read the installation instructions on bleeding the boiler to start. And look over your heating system. No doubt something straight forward.

 

[fixitflav]

Wasn't sure I understood the question about flow from the vent point on the boiler?

The system should have a number of manual air vent points, usually just a knurled nut to open. The one near the boiler will give some idea whether the boiler is full. Water should flow from the vent.

 

[chris watkins]

Darryl why do you think you are still capable of sorting this out & why no photos ?
If the boiler does the same thing when just the hot water is on (no heating) a small 22mm flow & return, then the problem lies on the primary circuit between the boiler & the upstairs cylinder cupboard. A flow meter is going to tell you what we already know & then what, what will you do to fix it?
Find someone who understands what they are doing, it is more than likely a simple fix as a number have suggested.
I am out of here, good luck.

 

[Darryl Pullen]

Thanks. I don't think I am capable of fixing it, I know I am not, just looking for some creative ideas and to learn a little really. Had two different plumbers out so far, 4k spent and the system is behaving identically, they tried all the "simple fixes" apparently and some more complex ones. Really appreciated the responses and ideas.

Tried to take some pics last night and all the useful bits are blocked by the big red pressure ball thing from the sealed system! Will try again or draw it down later.

 

[Harvest Fields]

Thanks. I don't think I am capable of fixing it, I know I am not, just looking for some creative ideas and to learn a little really. Had two different plumbers out so far, 4k spent and the system is behaving identically, they tried all the "simple fixes" apparently and some more complex ones. Really appreciated the responses and ideas.

Tried to take some pics last night and all the useful bits are blocked by the big red pressure ball thing from the sealed system! Will try again or draw it down later.

There’s your problem. You need a heating engineer and not a plumber mate.

 

[Darryl Pullen]

Valid point...

 

[Darryl Pullen]

 

[sammathias]

Oooosshh. How many copper pipes do you have coming from the boiler itself?