heat exchanger - Vaillant system bolier

[gastight]

I installed a system ( Vaillant system thermocompact 618/2 and Vantage cylinder) for customer about three years ago. System was flushed with X300 followed with inhibitor.
Got called his morning and ( customer just lives down the road) both heating and hot water is not working.
Went to have look and the boiler is cycling. It fires up and the flow gets very hot within 10s of seconds, return is cold.
So I

1. looked at the pump, works fines, i.e spins, resistance 160 ohms across the windings.

2. There are two NTC's on the flow and return near the heat exchanger The Resistance on the NTC on the flow is 3Kohms. The NTC on Return only has terminal, haven't come across this type before. Don't know how to check whether is working.

3. Suspect the heat exchanger is likley to be sludged. Took out, looks OK, Clean water came out both from the flow and return inlet.

4. Suspeced a blockage in the system somewhere but the autobypass on boiler is cold.

I am thinking it's the primary exchanger what's the best way of checking it. I don't do many boiler repairs mainly installs.

Thanks

 

[HarrogateGas]

Id be taking the pump head off to see if the impellor has come off.

 

[gastight]

I haven't taken the head off before although I replaced a failed pumps before. I think it's go four 'allan' screws. Will it come off easily if i undo them or would I have give it smack.

 

[GasAid]

Undo the bolts and with a small amount of leverage and it just pops off.

 

[Agile]

As you are so inexperienced with repairs you may be better off teaming up with a local RGI to do this kind of thing for you as it will be quicker and better for the owner.

Depending on the cause, it might be a chargeable call, or not!

I also agree that the pump impeller may be blocked or fallen off. It can fall off if the customer forgets to keep the system pressure topped up.

Tony

 

[gastight]

It doesn't seem to be the pump. Took the head off, impellor intact.

I think it's pointing to the HEAT exchanger.
I'll ring Vaillant tomorrow see what they say.

Agile - As I said I do occasional repairs, mainly for the people I do installs for and most of the time I can diagnose faults and carry out effective repairs.
This one seen seems to have me stumped. I try to work from first principles and assume nothing. in this case , the boiler switches on, run's for 20 second switches off, then after anticycle period starts again.
This points one of four things; pump, blockage in the system, blockage in the heat changer possibly the nTCS

1. Pumps spins, Resistence on windings 160Ohms and after Harrogate Gas sugestions checked impellor and it's intact
2. Blockage - the autobyass pipe inside does not get hot. and check all rads are fully opens, Three portvalve operates. Drained system as well water came out clean.
3. Heat Exchanger- took it out and looks OK and I am not sure how check it. This is first time I have taken Main heat exchanger out. Previously I've fixed faults on DHW heat exchanger - either replaced or descaled them with chemicals. But as this main heat exchanger and it's a systems boiler there shouldn't be any scale only sludge.
4. NTC's - measure resistence, it's about 3Kohms.

Any other suggestions/advice greatly appreciated.

 

[corgigazza]

If it is a blockage add kamco hyperflush to system leave for one week, then drain this cures most blockages also check the diverter valve as these tend to play up, with the motor not moving the diverter valve.

 

[Agile]

The single tag NTC.............

You measure resistance from tag to chassis, earth or whatever name you want to call it.

I think, but may be wrong that all Vaillant types are 1000 ohms at room temperature.

Tony

 

[gastight]

Heat Exchanger arrived to day and fitted. The bolier is now not locking out although it's taking a while for radiators to warm up.
I recommended a power flush but they don't want to have it done

What I don't understand how sludge could have built up. The pipework was cleaned with X300 and inhibitor was put in the systems.

What I drained the other day, water coming out clean. I can think they had drained system in the interim and not put any inhibitor in. They mentioned that Three port valve had failed and was replaced but not by me.

I have put X300 in again andwill let in run for a few days and then drain down and put some inhibitor.

 

[ChrisR]

NTC's - measure resistence, it's about 3Kohms.

Replace it then.

 

[Soggy_weetabix]

DS 40 will clean it up.

Just finished one today, and the water coming out would have been drinkable if it wasnt full of Fernox MB1

Im in a council property and am not allowed to touch my system...but...well, i have.

The engineer from Morgan & Phone asked my wife on the annual LLC why our system didnt give cause for concern, as the majority of tenants round here have, and I quote "bleed*n *****e systems.

She just said "I think we have a water softener".

DS 40 is very aggressive, and I know many plumbers who are scared of it, but whoa it does the job!

David