Honeywell motorised valve

[letshaveit]

I noticed that my rads were taking time before they started to warm up ie a= bout 10 minutes before any rise in temperature.

Checked the motorised valve and it appeared open ie the lever was forward b= ut there was a humming sound coming from it. The Grunfors pump was cold and= not making its usual volume of noise but putting a screwdriver on it and t= hen to my ear, I could hear it and it sounded that it was running.

Went to the boiler ( Vaillant Eco Pro) and the display was showing the temp= erature of around 41 deg C. (Incidentally it has its output temp set to 80 = deg). It would rise to 42 then the burner would moderate down to 40 - 41 th= en fire up again to 42. The output pipre from the boiler was only modoratel= y warm and the return was at ambient.

It then slowly went up in steps of one degree then moderated again. After l= ots of steps and 20 minutes later it has reached it set temp of 80 deg and = all seems happy- for the time being.

It seems strange to me but I'd like to seek an expert opinion.=20

Could it be a defective Honeywell valve or is the Grundfos pump on the bl= ink.

Please take into account that three rads were replaced about one month ago = so there may be some sludge about.

[John Rumm]

What layout of system is it, and how is it wired?

A valve not opening correctly could limit flow through the system - but in many systems that would also prevent the boiler firing since its often the micro-switch on the valve that fires the boiler.

the boiler have an internal bypass valve? (chances are it does). If the flow round the system is obstructed, then the bulk of the flow would end up passing through the bypass. So the boiler would see a very hot return - and hence modulate down.

[letshaveit]

about 10 minutes before any rise in temperature.

but there was a humming sound coming from it. The Grunfors pump was cold a= nd not making its usual volume of noise but putting a screwdriver on it and= then to my ear, I could hear it and it sounded that it was running.

mperature of around 41 deg C. (Incidentally it has its output temp set to 8=

0 deg). It would rise to 42 then the burner would moderate down to 40 - 41 = then fire up again to 42. The output pipre from the boiler was only modorat= ely warm and the return was at ambient.

lots of steps and 20 minutes later it has reached it set temp of 80 deg an= d all seems happy- for the time being.

o so there may be some sludge about.

[letshaveit]

It is an "S" plan layout and it has a bypass valve near the Grundfos pump a= s all the rads have TRVs. It's a Vaillant EcoMax Pro 18E.

I cant describe how it is wired in great detail but I remember clearly when= the engineer installed it originally he did it incorrectly so that when th= e control called for heat, the burner would fire up and then it would shut = down completely after about 5 seconds because there was no flow because the= pump hadnt been called into action. He got that fixed on day 2 and it worked perfectly ever since. I mention th= is because when there is no flow, the Vaillant shuts down completely and ha= s to be opened up and the reset button pushed.

[John Rumm]

Is this bypass just a manual valve or a proper spring loaded bypass valve?

There will be a difference between no flow due to a pump not operating and no flow due to a valve not opening (either at all or partially). Without the pump on, there will be no flow of water through the boiler at all. That will rapidly boil the small amount of trapped water in the heat exchanger, and the boiler will lockout due to an overtemperature condition.

With the pump running but a valve not open, there will be flow through the boiler because of the bypass valve. This will prevent the over temp and lockout, but will also mean that the heating circuit does not get a chance to dump much if any of the heat from the water. Hence the return temperature of the water to the boiler will quickly rise to close to the flow temperature. The boiler will have to respond by modulating its output down to minimum and / or cycling the burner on and off to prevent the maximum water temperature set point being exceeded.

If you have a situation where the valve for the heating circuit is only partially opening, you will get the situation with much of the flow running through the bypass, convincing the boiler to throttle right down, while only feeing heat into the rads slowly.

I would be inclined to verify if the CH valve is opening properly. If you look at:

a multimeter you should be able to detect mains voltage on the orange wire out of the valve when it is properly open. Normally the boiler should not fire until this wire is live, but its possible yours has been wired to fire on the presence of a demand from the room stat rather than the output of the switch on the valve.

Alternatively, you can take the cover off the valve, and then unscrew the screws that attach it to the wet part. This will expose the shaft that controls the valve itself. You should be able to rotate this back and forth relatively easily - possibly by hand, and certainly with pliers and not too much effort. If its very stiff, then you can lubricate the shaft and work it back and fourth a bit to free it off.

[Onetap]

about 10 minutes before any rise in temperature.

but there was a humming sound coming from it. The Grunfors pump was cold a= nd not making its usual volume of noise but putting a screwdriver on it and= then to my ear, I could hear it and it sounded that it was running.

mperature of around 41 deg C. (Incidentally it has its output temp set to 8=

0 deg). It would rise to 42 then the burner would moderate down to 40 - 41 = then fire up again to 42. The output pipre from the boiler was only modorat= ely warm and the return was at ambient.

lots of steps and 20 minutes later it has reached it set temp of 80 deg an= d all seems happy- for the time being.

o so there may be some sludge about.

Unscrew plug from front of pump, use a cloth to catch drips. Spin the pump = rotor with a screwdriver. If it feels 'stuck' and then frees up, that'll be the problem. Replace plug, fire up and report back.

[letshaveit]

It is an adjustable bypass with a turn knob and shows a scale from 0.0 bar = to 0.6 bar

I have a multimeter and will give this a check tomorrow morning but I must = admit it may be getting a wee bit close to my electrical competency level.

I monitored it again when I got back in this evening. Before it was due to = start, the return temp on the display was 12 deg. The Horstman timer for th= e CH side came on at due time and lit up the CH LED OK. Went out to the boi= ler ( in the garage) and it was doing nothing. Temp still at 12 deg. Went up to the where the cylinder is and the motorised valve appeared open = and it was making a subdued humming. The Grundfos pump was not running. Switched off the CH side of the Horstman timer and then back on. Checked al= l the bits, boiler, motorised valve and pump and all was the same as before= .

OK, I thought, lets see what happens when I turn on the HW side of the Hors= tman. It lit up OK. Checked on the boiler and it was running like a train a= nd so was the Grundfos pump.

I turned off the HW side and turned on the CH side and still nothing.

I left it like that and checked after 10 minutes . Nothing. Checked again after another 10 minutes and there it was working OK. The ret= urn was at 53 deg and rising!!

Hopefully this will narrow down the cause to either the Horstman or the val= ve. What do you think?

[John Rumm]

Basically stick it on AC volts, with a range >= 250V.

Stick the negative lead on a known neutral, and probe the other connections with the red one.

Probably easiest at the wiring centre or junction box if you have one.

Some humming is not unusual - but it might indicate its having difficulty moving...

OK

Right that proves the pump and boiler bit...

Do you know what the flow temperature was? (if you have an IR thermometer take readings from the pipes. Note if the pipes are unpainted, stick a bit of tape on the flow and return pipes and take readings from the tape since IR thermometers don't always get sensible readings straight off metal surfaces)

Well it sounds like the valve - but the sensible thing to do is follow the demand through from programmer to boiler.

You can do this all at the wiring centre by referring to the diagram I posted before. When the programmer is indicating "on" (terminal 4) for the CH there should be a live feed to the room stat. Turning the room stat up and down should make its demand click on and off. When its on the brown wire (terminal 5) to the valve should be live. The valve should then open (takes a few secs - you should here it winding round), and then the orange wire (terminal 10) should go live when it reaches fully open. That should then fire the boiler and possibly the pump (the boiler may drive the pump itself to allow it to overrun the pump)

If you can trace that through we should be much closer to a diagnosis.

[letshaveit]

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Hi John,

I got the multimeter out. Took cover off the Honeywell and found a double p= lastic connector block. One orange and one brown wire were connected toge= ther on one. Separately, on the other, was an another orange wire connectin= g to a blue wire.=20 With everything off, there was no voltage difference between them. When the= CH controller was activated, I registered 235 volts across. I heard the motor turn after a second or so and the valve opened, but there= was a slight ratcheting sound for about 4 seconds. The Grundfos pump start= ed up OK and when I checked the boiler it was running OK and the flow tempe= rature was rising steadily. It appeared to have worked perfectly. I had been on 15 minutes earlier and = every component in the system would still have been warm.

The CH was scheduled to come on at 06:00am this morning. Lying in bed I cou= ld hear the Honewell valve humming through the wall but I could not hear th= e usual circulation noise in the system. I got out of bed and checked the r= adiator at 6.15 and it was only half-warm - which suggested that it was doi= ng the slow stop start that I had first commented on.

To see if this problem only happens when its starting from cold, I will lea= ve it off until tonight and will monitor the startup again.

Meantime many thanks for your help.

Yvonne=20

[letshaveit]

Hi John,

I hoisted some photos of the valve and its surroundings.

I'm dreading having to replace it as it is behind the HW cylinder and is about

6" lower than the top of the cylinder.

From your experience, would it be possible to use a Jaw Dropper wrench on the nuts? It is a 28mm valve.

[John Rumm]

Yes there is often a little crimp terminal that joints the 5 core flex to the valve to the components of the motor head. I don't usually go probing in there - its typically easier at the other end of the cable in the wiring centre.

They often do that when you try to work out why they are not working ;-)

You may find that the valve moves more freely when warm...

Does the water heating come on as well at the same time? It could be the CH valve opens a bit and gets stuck, but the boiler is fired by a demand via the HW valve anyway?

My best guess at the minute is that the mechanical bit of the valve is a bit stiff... If that is the case its usually easy enough to fix.

Nice video on how to take the head off etc:

[letshaveit]

John, Many thanks for all your help. The system is up and running OK and all comes up to temperature quickly from cold. Nice to have a warm bedroom on a Sunday morning again :)

Regards

Yvonne

[John Rumm]

up to temperature quickly from cold.

No problem - sounds like a "sticky" valve that has freed itself.