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.

 

[Viper Gas]

Check direction of your rad valves and make sure flow is concurrent.

 

[Trotter31]

I noticed 2 gate valves in your photos.
Have you checked that BOTH open and close properly?
Just a thought!

 

[Bibbs118]

Bypass could be open.

The return from the cylinder should be the return nearest the boiler.

 

[sammathias]

Clutching at straws!

 

[kris]

If it was me id drain system ' remove gate valves make sure there fully open, if there ok id check zone valves and automatic bypass . If everything seems ok id disconnect flow and return near boiler and blast a compressor down ( shutting every rad apart from 1 and at one by now check airflow going round the flow and return . The fact it had a powerfully should be adequate but was it a machine or someone just pouring in chemicals ) there has to be a simple explanation even if tricky to find but a good engineer will find with out costing thousands .

 

[kris]

Just had a look at the pics of your system and tbh looks very diy ish and unprofessional. Don't take offence but there's a good chance it's simply the way it's piped that's causing issues .

 

[Harvest Fields]

If it were me, like I said before I would put a complete new flow and return in.

 

[doitmyself]

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.

I don't understand that

It appears that the Viessmann "expert" doesn't understand either.

The installation manual explains it like this:

Flow rate monitoring
Flow switch
The boiler is equipped with a flow switch for monitoring the minimum flow rate. The burner is shut down at a heating water flow rate below 200 l/h. No fault message is shown.
Recording the differential between the boiler water temperature and return temperature
The flow rate through the boiler is monitored by recording the differential between the boiler water temperature and the return temperature. Monitoring of the temperature spread with the boiler water temperature sensor and the return temperature sensor is an additional safety mechanism.
■ At a differential of > 25 K/< 30 K, the burner is operated at the lower heating output.
■ At a differential of > 30 K, the burner is switched off.
In such cases, check whether the heating system is adequately vented and the circulation pump is pumping sufficient
heating water.

200 litre/hr is equivalent to a differential of 35C at minimum output of 7.9kW.

 

[sammathias]

There was not veissmann engineer I'd say.

 

[Everal]

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

SOUND

 

[Everal]

Sounds like a circulation issue, pump could be at fault, causing boiler to overheat and cut out especially where so few radiators are getting warm

 

[gmartine]

Sounds like a circulation issue, pump could be at fault, causing boiler to overheat and cut out especially where so few radiators are getting warm

You resurrected a three month old, seven page thread for that? Congrats and see page 1.

 

[Everal]

You resurrected a three month old, seven page thread for that? Congrats and see page 1.

 

[rpm]

You resurrected a three month old, seven page thread for that? Congrats and see page 1.

Frustrating as it is, they are new, all excited and jumped in without reading the whole thread, better than a 7yr old post though

 

[Rob Foster]

Frustrating as it is, they are new, all excited and jumped in without reading the whole thread, better than a 7yr old post though

Agree I am a worn out 60 year old post, ultimately the more the merrier in my opinion , gmartine rocks for having a go
Rob Foster aka centralheatking

 

[Bibbs118]

Really, a pump may be the problem ? How would I go about testing that to make sure??????

 

[DAVE01]

just a bit of experience here but I have seen the chrome nut on front of pump were you vent pump there is a shaft behind this nut which indicates that pump is working but in fact it is not what I am saying is this spindle runs but the impeller stays put thus you have no circulating Nock off the two valves both side of pump loosen 4 allen screws run pump see what happens ? Impeller should run if it does not this is your problem

 

[fixitflav]

Nock off the two valves both side of pump loosen 4 allen screws run pump see what happens

Wouldn't you need to remove the 4 allen bolts to take pump head right off, so you can see the impeller turn (or not)?

 

[fixitflav]

The flow rate through the boiler is monitored by recording the differential between the boiler water temperature and the return temperature.

Don't get that bit. Only works if the heat input is known. Maybe gas flow is measured, or a relation between gas valve and flow is assumed, and h/ex efficiency assumed.

 

[doitmyself]

It's a safety mechanism, not a control one. If the differential is above 25C and below 30C the boiler automatically runs at minimum output. It the differential is 30C or greater the burner shuts down.

The main control mechanism is the flow temperature. If this rises above the set temperature it means that more heat is being generated than the radiators can emit, so the boiler modulates down until the temperature is correct.