DRAYTON ZA6 MOTORISED VALVE DOES NOT STOP FLOW

[CarlH]

This 28 mm 2-port valve is just over a year old and therefore has a detachable actuator. It is one of two Drayton 2-port motorised valves for this Drayton "Lifestyle Plan" of central heating layout. The dhw valve is a similar Drayton one, but a 22 mm.

For some time we have found radiators getting warm when the central heating side of the system is off, but when the dhw side is on and the cylinder thermostat is calling for heat (so the pump is running). This was not a problem with the original ZA6 (before this failed, owing to the valve spindle having gone very stiff). Nor was it, at first, with the present ZA6. It is nothing to do with the system design, which is the standard layout for this type and is well executed.

I have experimented by removing the actuator and holding the valve spindle very firmly in the closed position by clamping a very small adjustable spanner to it and putting pressure on this to hold the swinging valve paddle firmly in the closed position - using a piece of cord.

This showed that the valve is capable of closing completely. When the pump was running for the dhw, the pipe below the ZA6 was cold.

If I refit the actuator, which works correctly and appears to exert a pretty strong return spring pressure on the valve spindle (to hold it shut when the valve is off), when the dhw valve opens and the pump starts (lowest of the three speeds), the pipe below the ZA6 rapidly gets very hot. Clearly the valve is letting water past.

Possibly the problem is one of valve design. I have shown that the swinging paddle in the valve body is capable of holding its neoprene pad firmly enough against the port to keep the valve completely closed. But, in practice, it seems that the return spring pressure exerted by the actuator is not powerful enough to resist the pump pressure. The pump is normally on its slowest speed and the dhw circuit is all 22 mm pipe and has no modulating valve in it.

It is tiresome and expensive to have to change this valve yet again. Should I first try a new actuator, in case the present one is actually faulty rather then simply not exerting enough spring pressure? Even this is not a cheap solution, though it is far less trouble than changing the whole valve!

Or should I fit a Sunvic 28 mm valve in place of the Drayton? We have a Sunvic 2-port valve on a zone. This valve uses spring pressure to close it, but does not have a swinging paddle. It has a rotating cylinder (operating along the same lines as the ball in a ball-type gate valve or "Ballofix" valve). Therefore, when it is closed, it cannot be forced partly open by pump pressure.

 

[RickMoore]

Has the valve been fitted in the correct orientation. There should be an arrow which shows the correct flow tthrough the valve. If its the wrong way around this could cause it to hold open.

 

[CarlH]

Has the valve been fitted in the correct orientation. There should be an arrow which shows the correct flow tthrough the valve. If its the wrong way around this could cause it to hold open.

The installation is in the airing cupboard. The pipe containing each valve is vertical. The flow is from top to bottom. The pump is on the riser from the boiler. Above it, horizontal, is the Aerjec and the F&E pipe connection. Then the pipe turns down and splits into two branches, each containing a motorised valve. The 22 mm branch is the dhw primary circuit supply and the 28 mm branch the supply to the radiator circuit. It's a very simple and standard layout.

If the valve body were the wrong way round on the pipe the actuator would be upside down. It is the right way up.

The valve body does not have a flow arrow cast into, but the two ports are clearly marked A and B (on the back of the body). The fitting instructions state that the flow direction is from port A to port B, and this is how the valve body is fitted to the pipe: the flow direction is downwards in the pipe, and port A is at the top.

Because neither the valve spindle nor the retainer cast into the body for the actuator are central on the valve body you can fit the actuator only one way up relative to the body. If the valve is on a vertical pipe with a downward flow direction, as is the case here, the actuator should be upright, with the actuator manual lever at the top. It is.

You are right that it would be possible to fit the body the wrong way round on the pipe, but the fitting instructions are 100% clear on how it should be mounted and, even if I were not familiar with our system, it is clear in which direction the water flows in the vertical pipe from the pump.

If the valve were fitted the wrong way round, pump pressure would add to spring pressure to hold the paddle closed, so leakage past the paddle would not be a problem provided the neoprene sealing pad was in good condition. However, the valve motor might not be up to the additional load of opposing the flow from the pump as well as the force of the return spring, so might not succeed in holding the paddle open. Even if the motor exerted enough static torque to do this, the excessive load would probably cause it to overheat and eventually burn out.

Return spring pressure in the actuator normally holds the valve paddle closed. When the ch is on and its thermostat is calling for heat, the synchronous motor in the valve operates and forces the valve open against the return spring pressure. When the paddle reaches the end of its c.1/4 turn swing, the motor drops out of synchronism and holds the paddle in the open position.

 

[RickMoore]

What indicator are you using to tell the head is the right way around. There should be a arrow showing the correct flow direction through the valve on the valve body.
I get the impression that because the wrighting on the actuator is the right way around you thing it's the right way around. Those valves can be fitted up down and sideways. IF i'm understanding your description of the pipework and direction of flow, the valve needs turning upside down so to speak.

Could you post a couple of pictures up that would help get a better idea of your system.

 

[CarlH]

What indicator are you using to tell the head is the right way around. There should be a arrow showing the correct flow direction through the valve on the valve body.
I get the impression that because the wrighting on the actuator is the right way around you thing it's the right way around. Those valves can be fitted up down and sideways. IF i'm understanding your description of the pipework and direction of flow, the valve needs turning upside down so to speak.

Could you post a couple of pictures up that would help get a better idea of your system.

As already explained, on this Drayton valve body there is no flow direction arrow (just A and B port markings), but it can't possibly have been fitted the wrong way round, for all the reasons already stated.

Thank you for your concern, but the problem is not at the sort of "elementary mistake" level that you obviously suspect. What I am after is an opinion on (i) if I should spend (= probably waste) yet more money on a new actuator, to replace one that is only 18 months' old, or (ii) replace the whole valve with one which is not flow sensitive so cannot be forced slightly open by pump pressure (eg, a Sunvic 28 mm).

(i) avoids the labour and hassle of changing the whole valve, but would be a waste of money if the problem was not cured.

 

[RickMoore]

It wasn't already explained when I replied to your post before you edited yours.

Given that I would replace the valve entirely. A motorised full bore ball valve should prevent the same happening again.

 

[CarlH]

It wasn't already explained when I replied to your post before you edited yours.

Given that I would replace the valve entirely. A motorised full bore ball valve should prevent the same happening again.

Thanks, Rick!

Invensys technical suggest trying the actuator of the 22 mm valve on the 28 mm one. I will, but this assumes that the dhw valve actuator does not have the same problem - if it does, one is unlikely to notice as there are no radiators on the dhw primary circuit to get slightly warm!

I've checked the price of a new actuator: £50 to £60 pounds. It would be daft to splash out so much and find the same problem. Better to put it towards motorized full bore ball or cylinder (Sunvic) type valve, as you say.

BTW, the tech guy at Invensys eliminated the valve body filling with sludge as a possible cause of malfunction. Apparently this can happen if the valve is fitted to a horizontal pipe. He suspects the actuator on my ZA6 is weak on the spring return and says that what I describe is not a common problem. Of course, my valve dropped out of warranty in March 2013!

 

[Agile]

There is a possibility that the paddle is damaged and not creating a proper seal.

I think the heads are the same on the 22 mm and 28 mm heads so you could change them over if you seem inclined.

But I don't know why you seem intent on using less popular makes.

The Honeywell is the industry standard and give virtually no problems apart from eventual motor failures and they can be replaced easily too.

Tony

 

[nickso]

Invensys are wrong, it is a common problem.

Have you opened the actuator up yet?....the spring posts often break meaning it doesn't have proper spring force to keep it closed....this was more common on the older types before they beefed up the posts but it can still happen. Also check the plastic part of the fulcrum arm hasn't snapped off.

Your 22mm actuator will fit and work fine but I'm almost nearly 60% sure the 28mm valves were supplied with a 6 wire actuator.

You can also strip the paddle out of the body to inspect it. Just because you can hold it firmly shut with a spanner doesn't mean it will be the same with the springs if there is any damage to the paddle. New paddles are available.

 

[CarlH]

There is a possibility that the paddle is damaged and not creating a proper seal.

I think the heads are the same on the 22 mm and 28 mm heads so you could change them over if you seem inclined.

But I don't know why you seem intent on using less popular makes.

The Honeywell is the industry standard and give virtually no problems apart from eventual motor failures and they can be replaced easily too.

Tony

The central heating was modernized very radically in 1997, using Drayton's "Lifestyle" plan. Previously, the system (1968) had gravity hot water and pump for the rads only. The pump was in the large floor mounted boiler cabinet in the utility room and there were no motorized valves. There was no control (apart from the boiler's own thermostat) of the temperature of the dhw and no way of not heating the cylinder whenever the boiler was on. You could have hot water only or heating and hot water, but not heating only.

The Drayton plan converted the system to fully pumped. The pump and two (Drayton) motorised valves were sited in the airing cupboard. This created accessibility problems, especially as regards the dhw valve (ZA5), but freed up a lot of space for a radical refit of the utility room when the old Glow worm G75 boiler was replaced by a very compact wall mounted one (Ideal FF280).

After about 10 years the original ZA5 valve stopped working. I wasn't into doing such plumbing jobs myself at that time, and called in a plumber. Because of the position and immovable pipework, it was a VERY difficult job, and I reflected that the basic installation for the pump and valves had been done in 1997 with the cylinder out of the airing cupboard (the cylinder was changed as part of the modernisation. The new one is bulkier as it has non-removable insulation. At least with the old cylinder, even if it was not as well insulated, you could remove the jacket to improve access.)

The plumber who replaced the ZA5 brought a new ZA5 with him, so there was no discussion of alternatives. The new one, unlike the 1997 one, has a detachable actuator. This valve is still working fine.

The plumber commented that the detachable actuator was a helpful development. Well, it may be, but only if the actuator develops a fault, and not the valve itself! And an actuator is nearly as dear as a complete valve!!

For unconnected reasons I later discovered that the ports of Drayton and Honeywell 22 mm valves have a special ultra fine male thread, which is not the same (coarser) thread used as standard on 22 mm plumbing fittings. I don't know if this is still the case, but I found out that other makes, such as Sunvic, use the standard coarser thread. This could make replacing a Drayton valve (except possibly by a Honeywell!) even more difficult if it the olives were seized on to the pipes.

When the plastic mechanism in the integral actuator of the original ZA6 valve broke in 2012 I reluctantly bought a new (removable actuator) ZA6 because the Drayton 28 mm valves have female threaded ports, and I didn't know if other makes were the same. I feared that the Drayton male nuts might be impossible to remove because of seized olives, and did not want to have to cut back and remake 28 mm pipework. Sunvic's 28 mm 2-port spring return zone valve has male threaded ports, for example, so the nuts would have to be exchanged. In fact, I found I had worried unnecessarily. The olives were not tight on the pipe ends (they probably are now!)

I would be inclined to change the current ZA6 for a Sunvic, but am put off again by the potential problem of exchanging nuts etc.

I have not yet done the test suggested by Invensys technical (fitting the OK actuator from the ZA5 - I have checked it and it does shut off the ZA5 valve completely: no seepage past). However, even if this confirms that the ZA6 actuator is the problem, and not sticky operation of its valve spindle (manual test show no stickiness), I will not really feel confident enough about the current made-in-China Drayton ZA6 to splash out around £50 on a new actuator!

Honeywell's zone valves also use a swinging paddle, but the sealing head is a rubber ball rather than a neoprene pad. There seems to be potentially the same problem as with the Draytons. The spring return has to resist pump pressure when holding the pad/ball firmly enough onto the brass seat to prevent seepage past. The Sunvic design is, in theory, at least, superior in that the rotating valve piston cannot be turned by pump pressure. Confusingly, Sunvic refer to it as a "paddle", which is term used for the swinging arm in Drayton and Honeywell valves! When I fitted a Sunvic 22 mm valve elsewhere in our system in 2010 (a new zone for the kitchen etc) I was impressed the the full bore "cylindrical ball" (rotating piston) design of the valve itself, and by the fact that the return spring does not have to work against water pressure. It has only the job of rotating the "cylindrical ball" piston.

 

[CarlH]

Invensys are wrong, it is a common problem.

Have you opened the actuator up yet?....the spring posts often break meaning it doesn't have proper spring force to keep it closed....this was more common on the older types before they beefed up the posts but it can still happen. Also check the plastic part of the fulcrum arm hasn't snapped off.

Your 22mm actuator will fit and work fine but I'm almost nearly 60% sure the 28mm valves were supplied with a 6 wire actuator.

You can also strip the paddle out of the body to inspect it. Just because you can hold it firmly shut with a spanner doesn't mean it will be the same with the springs if there is any damage to the paddle. New paddles are available.

Well, Invesnsys would defend their own product, wouldn't they?! I'm not surprised if it is a common problem, given the design of the valve itself and the manner in which the paddle has to be held closed to pumped water pressure!

The spring seems fine, and clearly applies what appears to be reasonable force to the valve spindle. You feel this when you replace the actuator. The plastic posts are fine. I know about potential fragility of the plastic mechanism connecting the motor shaft to the valve spindle operating dog in the actuator. This was what caused the failure of the original ZA5.This ZA6 is only 18 months old.

My suspicion (to be confirmed or refuted by a check with the ZA5's actuator, now established as working correctly - please see my other reply), is that either the spring in the ZA6 actuator is below strength, or the valve spindle offers excessive resistance. The latter does not appear to be the case, but, as you say, manual tests do not replicate the force and behaviour of the return spring.

However, it is clear that the neoprene pad on the end of the paddle is capable of closing the port against pump pressure (it did so in my manual test) but does not close it firmly enough when the actuator is fitted.

I will report back further when I have tried the ZA5's actuator on the ZA6 valve. Yes, the ZA6, unlike the ZA5, has a 6 core harness, but the white core is not used in this 1997 Drayton "Lifestyle" plan. The NC contact in the thermostat is not used - only the NO contact (red or brown core to junction box and then brown core in harness to valve). Current through the NC contact in the thermostat would show "thermostat satisfied". I don't remember what function this might have as regards the actuator of the ZA6, but it would presumably be used if the zone valve had motorised, rather then spring, return.

 

[Agile]

I would be inclined to change the current ZA6 for a Sunvic, but am put off again by the potential problem of exchanging nuts etc.

Honeywell's zone valves also use a swinging paddle, but the sealing head is a rubber ball rather than a neoprene pad. There seems to be potentially the same problem as with the Draytons. The spring return has to resist pump pressure when holding the pad/ball firmly enough onto the brass seat to prevent seepage past.

You do seem very resistant to taking advice and want to replace with uncommon valves rather than the industry standard Honeywell.

Unfortunately, you have not realised that the Honeywell design is vastly superior to the paddle type.

The ball rotates at every operation so that a new face is presented and so wear and deformation does not occur.

You will be surprised to hear that a Honeywell I found letting by was because the ball had become seized and not rotating had formed a depression on the facing part of the ball!

Change over the head by all means but if you replace I strongly recommend a Honeywell.

Tony

 

[bikeman123]

You do seem very resistant to taking advice and want to replace with uncommon valves rather than the industry standard Honeywell.

Unfortunately, you have not realised that the Honeywell design is vastly superior to the paddle type.

I wont dispute what you say about the honeywell's valve operation as I know no different but I really must take issue with Honeywell's motorised head being 'the industry standard'. In my experience they are very unreliable and very expensive for what they are. They are only fitted in all new builds because builders get them cheap, then HW make a fortune on high priced replacements ripping off home owners when they fail frequently. Plumbers like HW parts because they provide a constant stream of work. As soon as someone makes a reliable motorised head that can be easily swoped in for the Honeywell head they will clean up.