Motorised valve stuck

[patagonia]

Paul Barker -

Thanks for all that. We don't have a vent pipe over the expansion tank any more, just a 28mm combined feed and vent pipe going into the side of the tank near the bottom if I remember correctly. So do I just need the bung for that? Iwonder why the heating engineer/plumber who smashed the tongues off the valve told us we'd have to drain down if we needed a whole new valve (which wd certainly take ages with our size house (l6 rads and 2 fan convectors) if it's possible to do it your way. If my kids weren't down here I think I'd move back to Yorkshire.

 

[patagonia]

Well, I replaced the motor and housing unit and guess what? It hasn't solved the problem. We still can't turn off the ground floor heating by turning the hall thermostat down or the programmer; the valve remains open and the boiler continues to fire. It is on and off like a yo-yo, switches itself off and then immediately tries to switch on, has several false attempts and eventually fires again till it turns off and the same thing happens again. Is this anything to do with the valve or is it caused by anything else? There doesn't seem to be much difference between the flow and return pipes at the boiler, which is set at the second highest setting, though one can feel a perceptible difference between radiator flow and returns (the correct 11degrees C. according to my device, which may, of course, not be accurate. Is this normal? We are obviously going to have to have a new motorised valve fitted which is quite beyond me. Would appreciate a reply from Paul Barker to my question on Saturday in response to his post saying it wasn't necessary to drain down to fit this. Do others agree with him on this? The plumber we had round before said we would have to drain down to fit one.

 

[ChrisR]

Did the spindle under the motor/head turn freely - they can seize.

Yes it's podssible to "suspend" the water in the system with the bungs, but some plumbers refuse to even try it after causing a couple of floods. The pipes can be frozen, most easily with an electric machine (£40 or so to hire) IF there's access to appropriate pipes. On a big system it can be worth it.

 

[patagonia]

Thanks ChrisR. I presume the spindle was the tiny brass upstand. I couldn't see it turning when I had the motor housing off but difficult to see in view of the location. How does one free it; presumably with the power off? Actually, come to think of it, I think I only watched it when I took the old one off before disconnecting the plug. As I couldn't see anything moving, I presumed it must be the motor. Perhaps I should take the new one off and have another look. I am wondering whether the plastic cog is a bit worn.

 

[patagonia]

Chris R

I note in your reply to someone else that you spoke of a spindle on top of a brass bit in the valve. When I took the top of our MV, there was only a tiny brass thing sticking up but it didn't have anything else attached to it that it turned. Should it have? It is a Siemens valve. I have just spoken to another plumber, unfortunately much too busy to help us (usual story) and he said (claims to be familiar with Siemens valves) that there is no way of freeing up a stuck valve and we will have to drain down and fit a new one. Am getting desperate as we are trying to sell our house and also going away for a couple of days at Christmas and would like to programme the heating to come on for a while so we don't have to comje back to a freezing house. The alternative is to leave it on all the time, day and night, which will be expensive, though I suppose I cd turn rad stats low and possibly the boiler low also so it doesn't get too icy. If I turn it off at the master switch the frost stat can't work.

 

[ChrisR]

There must be some sort of keyed shaft which connects the actuator to the valve. I can't remember Siemens one but if you look at the actuator base you'll see what moves.
Rotary ones often go stiff and sometimes can be improved with a squirt of wd40, and transverse or torsional positional variation (= twiddling).

 

[patagonia]

I was looking for something that moved in the base and wondered if the plumber had knocked a spindle off as the brass pin is so small one couldn't really see whether it turned or not. However, I have just had a look inside the old head and I see there is a brass cog which I presume is what is supposed to turn; this fits over the brass pin. I shall have to take the new head off again. If this cog is turning, then the problem is not in the head presumably and there must be a permanent live which is keeping the valve open, whether the zone stat is turned up or down. Is this a problem in the body of the valve or a wiring problem. I should be very unhappy if we got the system drained and replaced the valve at vast expense, assuming we can persuade anyone to do it this side of Easter, and found ourselves still in the same position.

 

[patagonia]

I finally got around to taking the new MV motor and housing unit off my Siemens MV, which didn't solve the problem when I put it on, and looked inside it and the brass spindle was going round so clearly the new RMH was a waste of time and money. Silly me had previously looked at the valve itself to see if anything was moving. Out of curiosity I plugged in the old motor h ousing and the cog moved in that as well. So could it be anything other than that the cogs of the plastic cog wheel in the valve have worn? Whatever, I presume it means a new valve. I still haven't managed to find a plumber who isn't booked up indefinitely.

 

[patagonia]

Having failed to cure our motorised valve problem by replacing the motor and housing and having failed to find a local heating firm who could come before Christmas, I thought I would take advantage of British Gas's fixed fee (£168) to cure one fault offer. I still had to wait till today for the engineer to visit. He had never seen a Siemens MV before and I had to tell him how to get the housing off and how they worked. All he did was to confirm what I already knew, i.e. that the problem was not with the motor. He said we would need a new valve which wd mean draining down (couldn't use a bung on our sized system) and that they he couldn't do this as it would take more than an hour and that's all they were allowed to spend. He didn't even quote me a price for doing the job on another day; just said I would get my money back. He said it wasn't necessary to put the motor housing back on the valve as he had fixed it open manually and departed. However, I found that as before if the hw and upstairs zone thermostats clicked off, the boiler stopped firing and the pump went offr so to get heat downstairs I had to put the motor housing back on and tie it down again, still in the manual on position. So much for Corgi training. Back to the yellow pages.

 

[D_Hailsham]

This might be useful: Siemens Valve Info

You say that you can hold the valve open and the boiler and pump works. How are you doing this?

There is an arrow on the body of the valve showing direction of flow; Port A=in, port B =out. Have you checked that the valve is the right way round?

 

[patagonia]

D Hailsham - What I did was to turn the zone stat off and (with the master switch turned off) put the lever into the manual on position and turn the power back on again. It means I have no thermostatic control,i.e. the boiler will fire and the pump will run even if I turn off this zone at the programmer but at least we have heating downstairs, even if the upstairs and hw are off. When the BG chap left the motor housing unit off, I think the lever jumped back out of the manual on position. At any rate the hot water wasn't circulating downstairs if the other zones were off, but if I tie the unit on (have to do this since the first plumber broke the tongues and clips off which hold it down) it does control the boiler and pump. Don't ask me to explain why. All I know is that despite the zone stat being turned off we can have heating dowstairs when only the downstairs is on. It does mean that we have to turn off the master switch at night and get up early to switch it back on. I have to say, however, tht the boiler is behaving in a very strange way, on most of the time, but making several false attempts to restart whenever it switches off. I don't know whether this is anything to do with the faulty valve or something else. Dreading the gas bill. The valve is a ZAV22.

Haven't checked the arrows and I am afraid I can't face untying the motor housing unit and taking it off again as there wd be nothing I cd do about it. As it has worked for yrs, however, I can only presume it is the right way round, though I think I did notice once that the hall rad got hot when the downstairs was off and the upstairs was on and possibly had just switched off. Long time ago so can't remember details.

 

[patagonia]

When I said it does control the boiler and pump, I should have said, to be precise, that it fires the boiler, which is only controlled by its own thermostat and I'm not sure that's working properly, and turn on the pump but it doesn't turn them off.

 

[D_Hailsham]

From what you say, I would suspect the valve has gone.

I am not familiar with this particular valve but, according to Siemens Instructions, when you put the slider to the Manual position, all you do is open the valve. The internal switch still stays open. This means that the boiler should not be able to work just by putting the switch to manual. But, as you say, it does. The only way this can happen is if the switch inside the valve is permanently closed providing a circuit to the valve.

To explain a bit more. All the zone thermostats do is control the motor. When the zone stat calls for heat it makes a circuit which runs the motor to open the valve. This makes the internal switch, which gets its power from a separate point not from the zone stat, close and provide power to boiler and pump.

So it would appear that the internal switch of the valve is permanently closed. This would also explain the noises you are getting. The pump is trying to send water through a closed valve and is battling against the closure spring.

Replace the complete valve. I suggest you get a Honeywell as they have the switch in the box on the top, not inside the valve. So, if there is a repeat of your problem, you just replace the switch assembly without having to drain down. (Though you won't be bothered about that if you manage to sell your house. )

 

[patagonia]

I suppose that's it though I can't understand how the hot water gets through a closed valve. I had assumed it had stuck in the open position. We only get the loud banging if we turn on he hall stat. It certainly makes sense to renew with a valve where one doesn't need to drain down to replace. Siemens tell me they also do one now. Still trying to get a heating firm. I fear we face a very large bill. Incidentally, the British Gas chap who came y'day said it was OK to have a combined feed and vent without any pipe going over the top of the expansion tank. Wish I knew what to do about the clanging noise in the pipes and upstairs rads when the upstairs stat turns itself on when the system is hot. Perhaps the answer is to leave the upstairs stat so it is on all the time and turn the trvs down a bit. Do you agree with someone who posted here that you don't save money by turning some rads off?

 

[D_Hailsham]

I suppose that's it though I can't understand how the hot water gets through a closed valve. I had assumed it had stuck in the open position. We only get the loud banging if we turn on the hall stat.

You could be right! Obviously when you tunr the hall stat on it is trying to move the valve and is failing.

Incidentally, the British Gas chap who came y'day said it was OK to have a combined feed and vent without any pipe going over the top of the expansion tank.

Yes, that's right. You either have a 15mm feed pipe with a 22mm vent hanging over the tank or you have a 22mm feed which also acts as the vent.

Wish I knew what to do about the clanging noise in the pipes and upstairs rads when the upstairs stat turns itself on when the system is hot. Perhaps the answer is to leave the upstairs stat so it is on all the time and turn the trvs down a bit.

Why not give it a try?

Do you agree with someone who posted here that you don't save money by turning some rads off?

Ths can cause a debate which can run and run. Let's say you shut the rad on an unused bedroom and shut the door. Heat will still enter the room through the doors and walls from the landing and the adjacent rooms. This heat will eventually escape through the outside walls. This means that the rads which are left on are being asked to heat up a larger space than they were designed for. This means that, if you keep the temperature in the heated rooms the same, you are likely to use more gas to heat them up. The alternative, to turn the temp down in the heated rooms is probably not acceptable. In general the best thing to do is to leave all rooms at their designed temperature.

One thing which heat loss calculators do not take into consideration is how people actually live. The calculators work out the heat loss from each room, including losses and gains between rooms; but they ignore the fact that there are doors between the rooms which are frequently open all the time. This means that, eventually the whole house stabilizes at one temperature. If different temperatures are set, say 21 downstairs and 18 upstairs, there will be a noticeable current of air flowing upstairs and someone will soon complain of draughts or that they are cold.