By-Pass Valve faulty?

[nodrog1]

I have a new Viessmann Vitodens 100 Boiler-working perfectly. I have a Honeywell Frostat and pipestat correctly installed. The system is S plan with a motorised valve for Hot Water and a motorised valve for heating. In between is a byepass valve set at 2.5. The frostat only activates the pump--the boiler just clicks and does not fire up. However if I latch either of the motorised valves the pump and the boiler will fire up. Does this indicate a faulty by-pass valve and how can it be tested?. The central heating and water heating are working perfectly.

 

[Brambles]

The probable cause is that the frost stat and pipe stat are not configured ( in parallel to the S plan) correctly to call for heat from the boiler.

 

[nodrog1]

Possibly-but the electrical "expert" from the company has re-inspected and says wiring is fine. I have found that with honeywell controller set to water "off" and heating set to "constant" the frostat does activate the boiler -which will give me peace of mind when I go on holiday in January as the boiler is in a cold garage and the house heating will be set to 12 degrees or so.

 

[centralheatking]

Just get a neighbour to park their car on your drive, give them a key and let them operate your system as they see fit. Thats what we do around here
centralheatking

 

[Ric2013]

It may be worth (if you're up to it) taking the actuator head off the motorised valves and manually turning the spindle to the open position on the valve itself and repeating your test.

This way, the motorised head will remain in the shut position and you can be sure whether the fact that the boiler will not fire is due to lack of flow, or whether it is down to the fact that, by opening the valve using the 'latch', you are actuating a valve microswitch.

I've known a bypass valve fail to shut properly, but to jam shut seems unlikely. That said, at 2.5 (metres head?) this may exceed the head your pump is running at by a long shot on a modern system. Looking at performance curves for the Alpha 2L range as an example of a reasonably modern pump, I can see that 2.5m head is only achieved in a constant pressure setting, or on the higher fixed-speed settings. On proportional pressure settings, you'll not get 2.5m head in no-flow conditions, and, in any case, a differential pressure automatic bypass valve will not work correctly with proportional pressure settings. Surprising how many installers cannot get their heads around this.

 

[Brambles]

Nodrog,

The Vitodens 100 - W has built in frost protection - which ( if weather compensation (wc) is fitted) is triggered through the external sensor. If no wc is fitted it will trigger when the boiler water temperature is less than 5 degrees C. This is completely independent of any external control system (except 240v supply to the boiler).

It is rather odd that your installer did not know this and installed a second system!!

Any additional frost stat and pipe stat should ONLY be wired through the External Controller if they are protecting pipes on the heating or hot water side of the motorised valves. That is unusual. If frost protection is required in that location trace heating would be preferable. Your additional frost stats appear to have been wired through the external (Honeywell) controller.

Any frost protection measures ahead of the valves, require the by pass to be fitted just ahead of the valves and the stat(s) should be wired ( as a zero volt connection) directly to terminals 1 and 2 on terminal X21 at the boiler. They should not be wired through the external controller. That is a job for a Gas Safe Registered engineer.

Having said that, provided that the bypass valve is correctly ( and set a a level below that of the internal boiler by pass located, the boilers internal frost protection control will protect that part of the system.

 

[centralheatking]

Possibly-but the electrical "expert" from the company has re-inspected and says wiring is fine. I have found that with honeywell controller set to water "off" and heating set to "constant" the frostat does activate the boiler -which will give me peace of mind when I go on holiday in January as the boiler is in a cold garage and the house heating will be set to 12 degrees or so.

I suppose what I forgot to post is just this, there are so many variables with this new control stuff, all the boilers, timers, room stats, cold weather monitors, zone valves and your fancy phone often do not interface properly, and then also go wrong anyway
Plumbers Forum recently is awash with these problems from all angles. The name of the game is heating your home and producing hot water..end of..stick to simple stuff for a few years until the technology is proven compatible...it is out there but its a question of which big boys will win. I know I am involved but would not buy anything just yet. centralheatking

 

[nodrog1]

Nodrog,

The Vitodens 100 - W has built in frost protection - which ( if weather compensation (wc) is fitted) is triggered through the external sensor. If no wc is fitted it will trigger when the boiler water temperature is less than 5 degrees C. This is completely independent of any external control system (except 240v supply to the boiler).

It is rather odd that your installer did not know this and installed a second system!!

Any additional frost stat and pipe stat should ONLY be wired through the External Controller if they are protecting pipes on the heating or hot water side of the motorised valves. That is unusual. If frost protection is required in that location trace heating would be preferable. Your additional frost stats appear to have been wired through the external (Honeywell) controller.

Any frost protection measures ahead of the valves, require the by pass to be fitted just ahead of the valves and the stat(s) should be wired ( as a zero volt connection) directly to terminals 1 and 2 on terminal X21 at the boiler. They should not be wired through the external controller. That is a job for a Gas Safe Registered engineer.

Having said that, provided that the bypass valve is correctly ( and set a a level below that of the internal boiler by pass located, the boilers internal frost protection control will protect that part of the system.

Many thanks and very interesting. I certainly knew about the -expensive-external sensor but I do not think the handbook(s) which came with the system made it clear that there is a -5 Degree sensor already installed. I will of course take it up with Viessmann. The installer is a trained Viessmann approved installer. Many thanks for your post.