Hot water thermostat opens/shuts valve, but no pump

[abenn]

Here's another puzzler for you: As part of my ongoing saga of heating coming on in the night when the controller's clock is "off", one of the BG engineers replaced the valve and actuator on the hot water tank. He described the original actuator as "motor on/motor off", but the new one is "motor on/spring off" like the heating zone valves. There's no maker's name that I can see, but it's labelled "BGMVSP-2".

After he left, I didn't have much hot water

Over the past few days I've determined that (a) the tank thermostat seems to open and close the valve correctly, but when it opens it doesn't trigger the pump to start, so I only get hot water if the pump and boiler are on because of heating demand, and (b) if the valve is closed and I open it by hand by pushing the lever on the actuator, the pump and boiler do start -- even if the programmer clock is "off" -- though, of course, the valve reverts back to its closed position as soon as I let go, and the pump then switches off

I'll be getting the engineer back next week, but in the meantime does anyone have any ideas how this could be happening please? I hate to see people just replacing parts, without knowing what's really going on.

 

[45yearsagasman]

Its a Drayton valve branded for BG. Not the best quality, but its what they use. It may well be faulty out of the box, has been known. Was it not checked before he left?
I'd be interested how he wired it.

 

[underwurlde]

Indeed, appears to be a wiring fault.

Or maybe a microswitch within the valve actuator not working...

if the valve is closed and I open it by hand by pushing the lever on the actuator, the pump and boiler do start -- even if the programmer clock is "off"

...but that is strange though.

Andy

 

[Dan Robinson]

Indeed, appears to be a wiring fault.

Or maybe a microswitch within the valve actuator not working...

if the valve is closed and I open it by hand by pushing the lever on the actuator, the pump and boiler do start -- even if the programmer clock is "off"

...but that is strange though.

Andy

Manual opening the valve by-passes the need for the clock.


What boiler is it?

 

[Agile]

Replacing a MOMO valve is not quite so straightforward. It needs a little thought.

He may have notes on his computer on how to do it. BG rely heavily on their computers having what they think is all the information that the engineer will even need for his work.

I would say he has wired it up wrongly!

Tony

 

[underwurlde]

Manual opening the valve by-passes the need for the clock.

I have yet to wake up this morning.

 

[45yearsagasman]

Is the other valve motor open and close?

 

[abenn]

Thanks for your suggestions -- incorrect wiring was my thought (I'm an engineer, but not the central heating variety) partly because the BG engineer had to phone a friend to figure out how to wire it, and partly because another engineer responding to my complaint about heating coming on in the night eventually found two loose wires, one of which seemed to be on the wrong terminal. Unfortunately he stopped checking the moment he thought he'd cured that problem, because at the time I didn't realise the hot water wasn't right.

Interestingly, the engineer who installed the new valve, and the subsequent one checking the other problem, both "verified" that the hot water valve was working properly by manually opening it and seeing the pump start up. Sounds like somebody needs to tell them that that bypasses the clock

 

[45yearsagasman]

http://wiki.diyfaq.org.uk/images/8/82/2PortMoMoValve.gif

 

[abenn]

Seems like two or three of us were typing at the same time

The central-heating valves (two zones) are now working correctly after the previous BG visits, so it's only the hot water valve that's a problem now.

I've got hot water most of the time because the tank heats up when the valve's open and the central heating starts the pump, but in this warmer weather the heating doesn't come on often so the hot water valve just sits in the open position with nothing happening.

Thanks for the link 45years... , but the valve is now a motor open/spring close type.

 

[45yearsagasman]

Yes, I realised that, but the link was only to show the difference in the wiring compared to spring return. Hope they sort it for you.

 

[abenn]

The end is nigh!! I wrote to BG customer services department last week, enclosing a log of my 2-year saga. On Friday a Lead Engineer came with the engineer that I'd booked to sort out the hot water. The engineer stayed all morning, found that the new hot water actuator had been wired incorrectly, but then the thermostat was not working so he replaced that -- I don't understand that one, for it had been opening and closing the valve even while it wasn't triggering the pump to start. He also checked and tidied up the wiring in the junction box that all the valves feed into.

Three days on and it's still working fine, and the whole system is quieter than it's ever been

 

[abenn]

Seems like I spoke too soon We came back from holiday at the beginning of the month, and the boiler and pump are starting up in the middle of the night again -- though this time none of the radiators heat up, apart from the one in the bathroom.

BG is on the case again, but I have one question for you guys:- Are there any quality gas central heating systems where the system can't start up if the programmer clock is "off"? The BG engineers keep telling me that it's "just the way the system works", that a sticking valve actuator can send a signal which will start the pump and boiler even though the clock is off. That just doesn't sound logical to me.

 

[Agile]

You seem to have difficulty in understanding the very simply wiring of a heating system where the motor valve is used as a relay to start the boiler. So a sticking valve will always start the boiler.

But most boilers have a feature whereby if they get cold they start the pump and if colder then the burner.

That is achieved using the boiler temperature sensors. So an out of calibration sensor or a high resistance lead can cause a false actuation of the frost protection. I suspect that is your problem.

But diagnosing that requires a good understanding of practical electronics.

It can always be the PCB itself but this is unlikely.

Tony Glazier

 

[abenn]

I understand the chain of events in normal operation -- thermostat says the area is too cold and opens a valve, which in turn starts the pump and boiler. But my valves aren't sticking (they're motor off, spring return) because they shut down successfully when the timer tells them to at 10:30pm (I usually check that everything's off before I turn in at about 11:30), and the boiler/pump don't start until some 4 or 5 hours later.

I understand too the bit about boiler sensors to protect it from frost etc., and for the need for them to be able to override the programmer's clock, but they've been replaced, the temperatures are relatively mild at the moment anyway, and my boiler's indoors at an ambient temperature that probably never goes below about 17 degrees C.

But the real reason for my question today is, if there's any control system where the programmer clock can't be overridden by the valves, I want it for my next heating system.