No hot water

[terryplumb]

Is the motorised valve on the pipework that goes to the coil ?
Have you previously been able to heat the cylinder and not have central heating ?

 

[cnikon]

It's on a larger 22mm pipe that I now assume goes to the CH and the coil, the system allows HW only or HW and central heating. Can't have central heating alone.

 

[Johntheo5]

It's on a larger 22mm pipe that I now assume goes to the CH and the coil, the system allows HW only or HW and central heating. Can't have central heating alone.

By that do you mean that you must select both HW & CH on together from the programmer to get the motorized valve to open?

The Honeywell ST 6300A programmer is a simple S system programmer with independent control or both operation of HW & CH so should have two motorized valves with their end switches connected in parallel to switch the boiler on/off, the HW temperature is then normally controlled by a cylinderstat strapped to the cylinder about a third the way up and should open/shut the HW motorized valve as required, similar for the CH control with a roomstat to switch the CH motorized valve on/off.

The HW cylinder tapstat will, if working, control the cylinder temperature but will not have any control over the boiler on/off.
Have you identified the white object (upside down) close to the tapstat?.

 

[terryplumb]

Have you identified the white object (upside down) close to the tapstat?.

Looks like a push fit stop end

 

[oldbutnotdead]

I'm not convinced that your plumber understands your older system design.
Unless there's another motorised valve somewhere, the usual deal was gravity circulation to the cylinder (so when the boiler fires the cylinder gets hot) and pump circulation to the radiators.
A wider pic of the pipework around the motorized valve would help

 

[cnikon]

Unfortunately the pipework defies logic, never seen another valve,but that doesn't mean anything! The "hot" pipe and the return disappear under the floorboards . At the moment we get heating and use the immersion for water, not ideal, but it will have to do for now.
The "system" was put in by a since retired plumber, Think he was the only person with knowledge of its peculiarities .

Thanks everyone

 

[cnikon]

By that do you mean that you must select both HW & CH on together from the programmer to get the motorized valve to open?

The Honeywell ST 6300A programmer is a simple S system programmer with independent control or both operation of HW & CH so should have two motorized valves with their end switches connected in parallel to switch the boiler on/off, the HW temperature is then normally controlled by a cylinderstat strapped to the cylinder about a third the way up and should open/shut the HW motorized valve as required, similar for the CH control with a roomstat to switch the CH motorized valve on/off.

The HW cylinder tapstat will, if working, control the cylinder temperature but will not have any control over the boiler on/off.
Have you identified the white object (upside down) close to the tapstat?.

Yes the hot water must be on for the central heating, I couldn't understand how one valve did all the work on its own. As stated later never seen another one. And it has worked for around 20 years, since we moved here, So who knows!

Many thanks for your advice

 

[fixitflav]

Yes the hot water must be on for the central heating, I couldn't understand how one valve did all the work on its own. As stated later never seen another one. And it has worked for around 20 years, since we moved here, So who knows!

Many thanks for your advice

You have 2 valves, the motorised valve for the CH, and the Taspstat (thanks to johntheo5 for the name). The Tapstat is actuated by the capillary and closes at a set cylinder temperature. It has no connection to anything else.
I assume when you want HW (and everything's working properly), when it reaches temperature the valve closes and water circulates through the bypass, and does that until HW goes off on the timer.
The Tapstat will have a bellows or diaphragm to operate the switch, and this can leak the fluid. If so, perhaps it fails closed (safer than fail-open and overheating the HW) and that might be your problem - new Tapstat. It doesn't give failure mode on the data sheet - does anybody know? Completely blocked coil seems unlikely.

It sounds like you also have a problem with the motorised valve actuator, but it shouldn't stop you getting HW, and I don't suppose you need CH at the moment.

 

[cnikon]

The tapstat looks just like a radiator valve, hot water seems to be present on both sides of it (by touch), I have loosened it so no pressure on the pin. The bypass valve is either open or shut manually, I opened it to check hot water return pipe right back to the boiler which seemed to prove thot pipe was not blocked. Maybe my tapstat is real, but it seems to operate just like a TRV valve, complete with pin in the body that presumably is depressed by the valve heating up, can't see how the by pass is operated as it is just as a manual valve. Your suggestions make sense, but my system doesn't , your help is much appreciated.

 

[fixitflav]

The tapstat looks just like a radiator valve, hot water seems to be present on both sides of it (by touch), I have loosened it so no pressure on the pin. The bypass valve is either open or shut manually, I opened it to check hot water return pipe right back to the boiler which seemed to prove thot pipe was not blocked. Maybe my tapstat is real, but it seems to operate just like a TRV valve, complete with pin in the body that presumably is depressed by the valve heating up, can't see how the by pass is operated as it is just as a manual valve. Your suggestions make sense, but my system doesn't , your help is much appreciated.

If you can remove the Tapstat and (temporarily) put a manual valve or something in its place, that would settle the question of Tapstat vs blocked coil. 1/4 turn ball valves are longer than gate valves so might be the right length. Doesn't need to be exact, the pipes will spring a little.
Is your bypass just a manual valve? A proper bypass isn't just a throttle, it passes little or no flow when there is somewhere else for the water to go, but opens more when necessary. If it's a manual valve it mustn't be closed, or when the motorised CH valve and the Tapstat are closed, the boiler will be deadheaded.

 

[cnikon]

My bypass valve is just on and off, as stated I opened it check flow in return pipe by bypassing the coil, the return pipe got hot all the way back to boiler. The bypass valve has always been shut since we have experienced this wonderful system (20 years). Unfortunately it seems what should be fitted, just isn't! I think a new cylinder is what is needed, but this one was only fitted in 2017, the old one had to be replaced due to a pinhole in the base, the coil was a long lasting one maybe? If this is ever sorted I will let you all know

 

[Johntheo5]

Can you remove the tapstat head completely and depress the pin, a reversed hammer is quite handy for this, just press the pin in with the hammer handle, the pin should then move back out under spring pressure. If you can't depress it, it may be stuck shut, just get a pliers and twist it back and forth while pulling on the pin, a squirt of WD40 or the like may help.
If the pin seems OK then you may have to grasp the nettle (pipe) and pull it back a touch after slackening the compression nut as suggested above, it would be a shame to throw out a maybe perfectly good cylinder if it was just air locked.
You have checked that there is water in the feed&expansion (small) tank in the attic?.

 

[cnikon]

Hi John, moved the pin with pliers, seems to be fully out, the plumber checked the header tank,and fitted a stop cock up there apparently for some reason. When you talk about the compression nut,do you mean where the return pipe connects to the cylinder? If I get brave enough lol, I think I should drain the system down a bit before loosening the nut. Can't do much at the moment as I managed to badly pull my rib muscles,and am very wary about employing another plumber.

 

[Johntheo5]

Yes, but Iwould first slacken and pull back on the flow (top) pipe and then try the return, it's really not difficult, don't drain down anything as you need the head to push out any (if present) air.
Its unlikely but if the header tank stop cock is installed on the supply to the system check that it is, in fact, open.

 

[fixitflav]

The bypass valve has always been shut since we have experienced this wonderful system

That's odd. If everything is working properly, some time in the last 20 years, the motorised valve and Tapstat will have both been closed, so no flow through the boiler, and some banging! Unless it's a big old-fashioned boiler that doesn't mind no flow, just goes off on its control-stat. In which case, not much need for a bypass at all.
I suppose the pump is working OK, is it?

it would be a shame to throw out a maybe perfectly good cylinder if it was just air locked.

There's an air release point shown on the pic with the Tapstat. If it's automatic there's lilely to be a way to open it manually. At a pinch, slacken the union. As you say, need to make sure the F/E tank is full (and the supply to it is open)..