Vaillant EcoTec 637 keeps switching off and on after 4 mins

[junior2012]

Hi,
I have a ecotec plus 637 that swicthes off after about 4 mins, recycles and then swtiches off after about 8 to 10 mins, even though the heat demand is on all the time. Also with the water demand on it does not come on at all. The boiler has been installed for about 2 years and has had no problems in the time. Any suggestions of what it could be? I thought the PCB may have a problem?

 

[Agile]

Have you had it serviced?

How long guarantee?

It may be a system/settings priblem

Tony

 

[junior2012]

Thanks Tony,

No The warranty has run out. The boiler was serviced a year ago.

 

[The831Bunny]

Turn the heating flow temperature on the boiler fascia (bottom large knob) till the display shows 70C and see if the radiators heat up. The temperature should change on the display as you turn the knob, then revert back to boiler temperature. 70C is the correct flow temperature for standard radiators and a modern hot water cylinder.

 

[bell824]

just to add to 831's post, when it goes off what temperature is the boiler showing, it sound's like it is going to anticycle mode and is not shifting the heat quick enough therefor causing the cycling.
has the boiler been installed as it was the biggest there and you could afford it (is it to big for system requirments).
as for the hot water could be as simple as a duff zone valve

 

[Agile]

You said with demand for HW the CH does not come on at all.

Thats could be because its been wired for hot water priority?

Tony

 

[junior2012]

Thanks 831 - The temp is already on max. This has not been changed in the time the boiler has been operational. When the boiler comes on, the rads do heat up, the problem is that it goes into anticylcing after 4 mins and does not come back on for another 8 to 10 mins.

Thanks bell824 - The boiler is servicing 14 rads in a six bed house, It was what was recommended. I dont know if its too big, but it has been working fine for over 2 years. Any other ideas. There are 3 valves and with all 3 zones putting out a demand, the valves open fully, but the boiler goes on/off every few mins. The only exception is that when only HW is on demand and the valve for that is open, the boiler does not come on at all.

Thhnaks Agile - Sorry I meant that with HW on demand, the BOILER does not come on at all.

 

[Agile]

Is the HW valve opening? If not its faulty!

If valve is opening but not bringimg on the boiler then its probably faulty too but could be a wiring fault.

Locking that MV open will heat water when heating is on.

Sounds as if the pump is failing or impeller is blocked. Accessing that should be by an RGI.

Tony Glazier

 

[The831Bunny]

Hi. As Bell said earlier you do need to check what temperature the boiler is turning off at. It could be as simple as a broken temp knob. With the boiler on maximum heating temperature the boiler should turn off around 75C. I would doubt the pump is slow/blocked because that would throw up F.75 fault codes, although it is sounding like a circulation problem on the system.

Plenty of educated guesses from us on the other side of a keyboard, but it's so much easier to get a reliable boiler engineer in front of it. Usually this sort of thing can be diagnosed in under 10mins.

 

[Agile]

This boiler needs 28 mm pipework but with only one valve open it will then be connected to a single 22 mm circuit which the boiler will not like.

However, it was working before so something has obviously changed.

Tony