fauly mid point valve or something else?

[dave2410]

I have an open vented gravity fed system operated by a baxi bermuda 401 back boiler and trv's on all rads except one. About a week ago I bled a couple of rads but with the central heating on . That evening I came home to check if rads were ok and found that none were working. My initial thoughts were that I had an airlock in the system. I have now bled all rads and also the pump, although no air or water was released from the pump. The spindle inside the pump was spinning fast and quietly. The F&E tank in the loft has water in it and appears ok. I have an old ACL Lifestyle midpoint motorised valve on the system and neither the manual valve on the side or the lever for W M H can be moved at all. I am a total novice and have only checked these things from looking for advise on the web. The lever on side of motorised valve is stuck on H and will not budge, also the manual lever is impossible to move. Before I go and purchase a replacement valve are there any other checks I can carry out to see if the fault lies elsewhere, although from what I have read I think the mid point valve will need replacing regardless. Thanks.

 

[D_Hailsham]

The 'lever' under W M H is just an indicator of which position the valve is in. From what you say it is in the H (heating) position.

Turn off the power to the system at the main switch; setting the HW and CH timers to OFF is not sufficient.

The valve should move back to the Hot Water position (W).

The lever in the slot should be at the AUTO end.

Try moving the lever along the slot to the MAN end.

You should feel some resistance and hear the mechanism whirring

The lever should return to AUTO end when released.

If OK turn system back on and try again.

But If the lever is loose in the slot, the valve has stuck.

Unfortunately ACL Lifestyle valves are no longer available and can't be repaired, so it will be new valve time. Get a Honeywell V4073 installed.

 

[dave2410]

Hi D_H, thanks for the advise. I will give this a try this evening when I get home. Will report back with my findings.

 

[dave2410]

Well I followed the instructions given by D_H and it did seem to reset the midpoint valve. However, when I turned on the system again I still got no heating or hot water? The boiler stat was set to high and did fire up initially but did not remain on for too long. I did not leave the system on for too long (15-20 mins) for fear of doing damage. I will try bleeding rads and pump again this morning, this time with the system off and then try system again tonight. Any other thoughts will be gratefully taken on board.

 

[D_Hailsham]

Well I followed the instructions given by D_H and it did seem to reset the midpoint valve.

Are you saying that the valve passed all the tests I suggested? i.e there was resistance when you moved the lever from Auto to Man and it returned to Auto when released.

If it passed all the tests, the valve is not sticking.

Can you get heating when the HW cylinder is being heated? Turn the cylinder stat up to make sure there is a demand for heat.

 

[Agile]

Based on what is written here, which may not be comprehensive, the pump is running but not the boiler.

That is usually just connected in parallel with the pump on those old installations.

Tony

 

[dave2410]

D_H - Yes, the valve did seem to pass all your tests, however, when I tried it again this morning for a short while, when the programmer came to the end of its timed cycle the lever on side of valve did not revert back to the W position. I turned it off from the mains again and then the lever returned to W and also manual lever could be moved and the mechanism from within could be heard to be turning.
When I tried turning the heating on last night and again this morning, with the boiler stat turned to "high" it did fire up but only remained on for about 5 mins if that. Once the boiler had switched off the pump in the airing cupboard still remained on for the duration of time set on the programmer. When this all started last week the pump did get very hot but was not making any "alarming noises" just an audible hum, not a long drawn out hum at the same level but continous in short bursts.
Agile - "the pump is running but not the boiler" ??? As mentioned earlier I am a complete novice and only gleaning little bits of info as I go along. The boiler is overdue a service and an engineer is booked in for this coming Friday morning although it would be nice to get some heating around the house before then if possible. Any further thoughts on what I could try?

 

[D_Hailsham]

D_H - Yes, the valve did seem to pass all your tests, however, when I tried it again this morning for a short while, when the programmer came to the end of its timed cycle the lever on side of valve did not revert back to the W position. I turned it off from the mains again and then the lever returned to W and also manual lever could be moved and the mechanism from within could be heard to be turning.

If the valve is in the 'H' (heating only position) when the timer or room thermostat turns the boiler off, then it will stay in that position. Just a 'feature' of mid-position valves. It will revert to the 'W' position when either there is a call for Hot Water, or the power is completely turned off. So what you saw was normal behaviour.

When I tried turning the heating on last night and again this morning, with the boiler stat turned to "high" it did fire up but only remained on for about 5 mins if that. Once the boiler had switched off the pump in the airing cupboard still remained on for the duration of time set on the programmer.

The boiler and pump are controlled by the room stat. But the boiler is also controlled by the boiler stat. If the boiler is overheating the boiler stat will turn the boiler off, even if the room stat is calling for heat. So your symptoms will occur - boiler off and pump running.

Several possibilities: lack of water; blocked heat exchanger; faulty boiler stat; faulty pump; faulty gas valve.

The service engineer should be able to sort it out. Not something one can positively diagnose at a distance.

 

[dave2410]

Thanks for your advise anyway D_H. Will have to see what the engineer uncovers on Friday.