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

[Darryl Pullen]

Hi,

Was hoping to get some advice... When I moved in the central heating was not working (they didn't tell us), paid quite a bit of cash to get it looked at, everything pointed at flow problems as the "Ideal" boiler would display flow error code. In the end, the plumber let me down, so went with another plumber and decided to install brand new boiler, a Viessmann Vitodens 100-w.

Basically, 2 years on, still having the same problems. It was open vented, but has been converted to sealed system, doesn't lose pressure. Had new pumps (currently got Grundfos Alpha2L 15-60 (130)), and still not getting any heat into the rads. We have 12 rads, 3 large ones, all doubles. Most have TRVs.

The boiler starts up, shoots up to 50 degrees quite quickly and cuts out, then repeats. Oddly it does this even on hot water, a much much shorter circuit. Eventually the hot water does heat up a little bit. Today I started it up to see if it was working (as it was sort of "working" over the winter, but badly), and it just short cycles as above, no heat into any rads after 45 mins of running. The heat/burner display has never ever been above 1 (out of 4 or 5 levels).

It has been power flushed (although not sure how well), and various other bits of work and has eaten a ton of money. have tried balancing but something more fundamental is wrong I thing, or this boiler is just terrible. Also, doesn't seem to be air in the system as it is sealed now, and never any air in rads at all, immediate water trickles out (very clear water).

I am a bit desperate now as I honestly don't know what to do next, can't keep throwing money at it... Any advice really is much appreciated. Hoping someone might be able to help.

 

[ShaunCorbs]

Sounds like you need a engy to look over the system could be a pump or a blockage as it sounds like its not circulating

 

[Karl]

Really sounds as if the system is badly blocked, or something stupid like an isolator out of view turned off maybe. If it was me I would take a radiator off make sure all other rads are isolated put a hose on radiator pipe and see if you get flow when filling system (as long as filling loop is on boiler) test both pipes on radiator this way, if no luck try on a couple other radiators at opposite ends of system. If pipes are that badly blocked then it might be cheaper to replace pipe work and is it any chance micro-bore pipes? Can’t believe someone has fitted you a new boiler and walked away without the system working!

 

[AMGasServices]

Do your flow and return pipes get warm under the boiler ?

How far can you trace these pipes ? Check if they’re heating up.

Do you have a hot water tank in the house ? If so Please post pictures of this.

 

[rpm]

Microbore pipe anyone?

 

[Darryl Pullen]

Hi all, no microbore in the system. It does have a hot water tank (will try and grab some pics tomorrow). The ground floor pipes are mostly under screed. There are three returns, hot water, upstairs and downstairs rads. The system has been working, and have had heat into all radiators, but always been slow and rubbish. The more rads I turn off, the better the boiler performs (as in, it cuts out less).

When it was powerflushed (with the boiler on) heat got into every rad within seconds. And when the hot water turns on for the first time, the boiler heats up for a bit, heat comes in to the return, and yet the boiler still cuts out!

I have never ever had a "hot" return pipe coming up from the floor (the downstairs return), the hot water return has been hot, and the upstairs return has been hot too. But at the moment it just cuts out and heat never gets into the return. Flow gets hot while heating, then quickly goes cold when cut-out.

 

[Darryl Pullen]

All three return pipes meet in the boiler cupboard near the boiler. Boiler is downstairs in garage, pump is upstairs in airing cupboard. Pump is on full, anything less and the system is even worse.

Was wondering if it is possible to put a secondary pump on the return. Or if there is any clever way to actually determine if there really is a flow problem, like flow meters strategically placed??

 

[rpm]

Microbore pipe anyone?

Well that didn't help so would a thermo camera help?

 

[chris watkins]

There are flow meters available, Caleffi do a good one.
It does sound like you may benefit from hydraulic separation of the boiler & the system but a good heating man would need to have a look at the system layout as these 3 returns don't sound quite right
Balancing valve with flow meter

 

[chris watkins]

Nothing wrong with the Viessmann Vitodens, well at least there wasn't until someone was power flushing through it.

 

[townfanjon]

You need to check if there is a temp difference back at the boiler before spending anymore money .

 

[chris watkins]

Just a thought but when the system was converted to a sealed one was the old pipework around the tee's to the open vent / cold feed removed or were they left in & capped / adapted?
It sounds like there is a large restriction somewhere & power flushing does not always clear them.

 

[Best]

I had one job that had similar problem which I eventually discovered had a seized motorised valve below a floor.
Not saying that is possible on this occasion, but just putting out that point.

 

[Darryl Pullen]

Thanks for taking the time to reply. When converted to sealed, the old stuff was removed (F/E tank) and capped off.

Does it not sound normal to have 3 returns converging at the boiler, one comes up out of the screed, and two from upstairs. One other thing the return on most of the radiators (or all) is always cold. So def is a problem with return. But none of it makes sense when you add all the symptoms together.

It's hard to comment on the temperature difference between flow and return at the boiler as it doesn't stay on long enough to get good heat into the system, but when it has been working the flow is always hot, return lukewarm to warm (after hours of running). The boiler always "kettles" on starting up too.

Everything keeps telling me it needs a bigger pump, or secondary pump on the return, or possible another more thorough powerflush (or a powderflush?!). Don't mind spending a bit more on it, but just have no idea what should be the next move.

 

[Harvest Fields]

Thanks for taking the time to reply. When converted to sealed, the old stuff was removed (F/E tank) and capped off.

Does it not sound normal to have 3 returns converging at the boiler, one comes up out of the screed, and two from upstairs. One other thing the return on most of the radiators (or all) is always cold. So def is a problem with return. But none of it makes sense when you add all the symptoms together.

It's hard to comment on the temperature difference between flow and return at the boiler as it doesn't stay on long enough to get good heat into the system, but when it has been working the flow is always hot, return lukewarm to warm (after hours of running). The boiler always "kettles" on starting up too.

Everything keeps telling me it needs a bigger pump, or secondary pump on the return, or possible another more thorough powerflush (or a powderflush?!). Don't mind spending a bit more on it, but just have no idea what should be the next move.

I would Scrap the old flow and return and start again.

 

[Darryl Pullen]

As in, get them fully re-piped? I guess I would have to get the whole downstairs re-piped as it is all under screed.

 

[chris watkins]

Darryl the problem isn't the return it is the circulation around the circuit/s i.e. flow rate (amount of water going past the boiler to carry the heat away)
Putting another pump on the system is not going to be the answer either, all that will do is increase the push but not the flow rate.
If the first power flush didn't work why do you think anther one will?

From the posts so far you should understand that there is no simple fix, without being able to see the system layout we can't take this any further.
A 12 rad system is not that large & the 15/60 should be able to deliver the required flow rate to this.
With all the rads turned off (and the heating zone valves shut) dose the heat flow between the boiler & the hot water cylinder above? if not then you need to get a heating engineer in.
Where are you based perhaps someone on here could help?

 

[Darryl Pullen]

Understood, and thanks for the advice. I know they replaced all ras with doubles, so wanted to check the pump was man enough for 9 doubles, 3 of which are huge 2m ones. Sounds like it should be.

Maybe time for a full re-pipe!!

 

[sammathias]

They replaced all the rads and powerflushed...sounds like a blockage or valve/pump fault

 

[Harvest Fields]

Are both valve on each radiator fully open?

 

[Darryl Pullen]

They are not all fully open, although yesterday went round and opened most up. It the past it behaved better with some turned off completely, and with them balanced a bit.

 

[Harvest Fields]

Remember the position of them all by writing them down then open them all fully. Then close them all apart from one and see if that one gets hot all the way back to the boiler then close that one and open another until you get to the last rad

 

[Darryl Pullen]

Thanks, will do that. I always read start with the one closest to the boiler, but think I need to start with one close to the pump (which is upstairs)? Never know which is first in line. But will shut them all off tonight and try. What would it tell me if it works fine with just one radiator! (which I think it might)...

 

[Harvest Fields]

Thanks, will do that. I always read start with the one closest to the boiler, but think I need to start with one close to the pump (which is upstairs)? Never know which is first in line. But will shut them all off tonight and try. What would it tell me if it works fine with just one radiator! (which I think it might).

Not a lot you need to do each rad one at a time

 

[Best]

You have very slow flow in the circuits and that is why balancing and turning some rads was appearing to help the system work better.
It could be a part blockage or a valve somewhere nearly closed.
It can be in the flow or return and the return being cool proves nothing.
Have any of the tee off connections on the return where old cylinder etc was checked for blockages. A strong magnet out against a copper fitting or pipe will suggest magnetite at that point if the magnet is pulled to the pipe/fitting.