Hot water too hot.

[ericmark]

I never saw significant advantage in Y-plan.

The fact it never turns off, there is always a path for water to flow, so the boiler could naturally cool with thermo-syphon. Same is true for C Plan of course. I have seen pumps fail where with S plan the micro switch has stuck and pump and boiler left running, the boiler will turn off with over temperature but pump pushing against a closed valve.

Today we have TRV's on all radiators so need a by-pass valve, but when Y plan came out we did not have TRV's or by-pass valves.

 

[DP]

That is, or could be, the problem. Without studying the mid-position valve operation in detail, I would think if something goes wrong it defaults to the HW position, like the either/or W-plan valve. So if CH is calling, the cylinder gets overheated.

If valve is faulty, heating would not come on. I think you need to look at the valve operation to see why or how the water is heated.
Previously water was at desired temperature because boiler was set to lower operational temperature and cylinder stat was never satisfied. Now with boiler at higher temperature, water at top of the cylinder is much hotter while the thermostat may be disconnecting the circuit having tripped at desired setting

 

[DP]

In normal operation, yes, but isn't it possible for a faulty valve to leave the port to the cylinder open, although the cylinder stat is satisfied?

Ok……..what do you think is going to happen to the cylinder thermostat when the temperature exceeds the stat setting. Bear in mind it is the thermostat on the cylinder that fires the boiler NOT the valve which does NOT even move

 

[fixitflav]

Today we have TRV's on all radiators so need a by-pass valve, but when Y plan came out we did not have TRV's or by-pass valves.

Same with W-plan. If you have TRVs on all rads you need a bypass, but not if one (or more) rads does not have a TRV. I believe the regs say there must be a roomstat, and it would go in the room without a TRV.

 

[fixitflav]

Ok……..what do you think is going to happen to the cylinder thermostat when the temperature exceeds the stat setting.

If it's working properly the contacts open, and if there is no CH called, the boiler stops. If there is CH called, the valve (if working properly) closes the HW port and the boiler continues to fire. If the valve is faulty so doesn't close the HW port, the cylinder can overheat.

Bear in mind it is the thermostat on the cylinder that fires the boiler NOT the valve which does NOT even move

That's true but you said

If valve is faulty, heating would not come on.

That's inconsistent. It's the cylinder stat that fires the boiler, faulty valve wouldn't prevent it firing.

Previously water was at desired temperature because boiler was set to lower operational temperature and cylinder stat was never satisfied.

AFAI can see, the OP has not said that. It would be an odd way to run the system - HW temperature controlled by the boiler control-stat, firing on/off all the time HW is called on the programmer.

 

[DP]

If it's working properly the contacts open, and if there is no CH called, the boiler stops. If there is CH called, the valve (if working properly) closes the HW port and the boiler continues to fire. If the valve is faulty so doesn't close the HW port, the cylinder can overheat.

You are forgetting in mid position the cylinder thermostat runs the boiler not the valve
Only when hw port closed does the valve run the boiler

AFAI can see, the OP has not said that. It would be an odd way to run the system - HW temperature controlled by the boiler control-stat, firing on/off all the time HW is called on the programmer.

You may want to reread the first post of this thread

 

[ericmark]

Same with W-plan. If you have TRVs on all rads you need a bypass, but not if one (or more) rads does not have a TRV. I believe the regs say there must be a roomstat, and it would go in the room without a TRV.

A TRV is a room thermostat they also form zones.

 

[fixitflav]

You may want to reread the first post of this thread

Fair enough, I hadn't re-read that. But I'd be surprised if the OP meant he turned the boiler control-stat up when the weather got cold, and not just turned on CH on the programmer, and/or turned up the roomstat.

Perhaps he'll confirm.

 

[Ihavenojob]

Has the OP actually taken the temperature of the water at a tap ? First thing I used to do when customers complained of water too hot or not hot enough. As someone posted, with the boiler stat low , the cylinder stat may not have reached temperature, now the boiler stat is turned higher, the water in the cylinder may now be reaching the set (higher) temperature.

 

[ericmark]

To my mine 60 - 65°C is too hot at the taps, but under that temperature you can get legionnaires, so that is normally the minimum setting so @Ihavenojob comments are valid.

As to by-pass they will not work if the pump is on the return, so not all systems have a by-pass, not sure what would happen if the pump runs with all TVR's closed when on return, cavitation I would think. On the feed the pump fails, I have seen that when a motorised valve micro switch has failed. Boiler turns off on over temperature.

The one radiator without TRV is often the bathroom, it is in my house, but the bathroom is on thermo-syphon with the DHW, so does not help. And you would not fit a wall thermostat in a bathroom for whole house.

But back to basic question, if the hot water stays cool when turned off at programmer then not the valve, but the reverse is not true. The manual lever on the valve only takes it half way, some have an indicator, and some you can remove the head to check.

 

[dannynolan]

Fair enough, I hadn't re-read that. But I'd be surprised if the OP meant he turned the boiler control-stat up when the weather got cold, and not just turned on CH on the programmer, and/or turned up the roomstat.

Perhaps he'll confirm.

No we did turn up the boiler control stat as the radiators weren't hot enough.

We emptied the hot water this morning and turned on the CH at the programmer but not the hot water. The hot water pipes stayed cold. So from what you are all saying it looks as though the cylinder stat may be the problem. Right?

 

[fixitflav]

No we did turn up the boiler control stat as the radiators weren't hot enough.

OK I stand corrected

We emptied the hot water this morning and turned on the CH at the programmer but not the hot water. The hot water pipes stayed cold. So from what you are all saying it looks as though the cylinder stat may be the problem. Right?

Looks like it. I suppose the next test is to call for HW and check the pipe to the cylinder get hot. If so it seems the cylinder stat contacts are stuck together. In that case the boiler is powered all the time HW is called on the programmer (going on/off on control-stat). Does that happen? You might be able to take the cylinder stat apart and clean up the contacts. Good luck!

 

[Dereekoo]

You might be able to take the cylinder stat apart and clean up the contacts.

Or bite the bullet and spend £16 on a new stat

 

[fixitflav]

Or bite the bullet and spend £16 on a new stat

Just a suggestion. It's his choice

 

[Harry Bloomfield]

Or bite the bullet and spend £16 on a new stat

The lack of it clicking was an obvious sign the stat wasn't working.