Why is my boiler on...when it should be off?

[Tiggsy]

My boiler programmer has hot water on for 2 hrs in the morning and heating the same...right now, it is all off.

However, every now and then the boiler kicks in for a few minutes....also, related??? the hot water tank is ALWAYS too hot to touch (nice for warm towels in the airing cupboard...but is that right???)

Should the boiler fire up when the programmer says its off??

[anonymous-user]

Where is the boiler? If it's in a garage or other cold room then it may have a frost stat which kicks in when the temperature goes below a certain point.

[Tiggsy]

in the kitchen...which is 20 degrees!

[Busterbulldog]

sticking zone valve

[Sowler]

Got an Eco option button on the boiler? If so is it off. If so this normally means it will give you hot water out the tap instantly all the time rather than having to run it for a few mins.

[Tiggsy]

That would keep the tank boiling and have the boiler kick in and out all day? Rads are all fine, ie. off right now.

[jdw1234]

I had this sort of problem the other week.

It was a sticking valve as someone has stated above.

[shtu]

Busterbulldog said:

sticking zone valve

Almost certainly this, it's by far the most common cause.

[Tiggsy]

ok - to my dumb mind sticking suggests it stuck open? if thats the case, why does the boiler come off and on??? - or is it still reading the stat on the outside of the tank??? In fact, given that the tank is boiling - have I got a screwed tank stat too???

[Rickyy]

Sounds like a sticking valve. Especially common with Drayton zone valves.

The boiler keeps firing because it is being powered by the micro switch inside the zone valve. The only thing that will be shutting the boiler down is its own control thermostat (there should be a knob on the front to alter this).

[Tiggsy]

ok...but as my boiler is boiling.....why would the stat call for more water, zone valve stuck or not???

[essayer]

CH/DW systems are all quite dumb really, it's usually
Thermostat asks for heat & timer on = gate valve motors to open

Gate valve, when open, makes a connection which tells the boiler to produce heat

When stat reaches temperature the zone valve closes, breaks the connection and the boiler switches off

So if the valve is stuck on then the boiler will keep firing until it overheads and turns off .. Etc

[Tiggsy]

ok...but my boiler only fires now and then....so if the valve is stuck open, wouldnt the boiler be stuck on? or could the stat still over ride that?

[essayer]

The boiler will fire until it gets too hot, at which point it will turn off until it cools down, and repeats over and over. Not sure how your system is wired, maybe the pump isn't running so the boiler will overheat quickly
If you do actually need hot water it will work properly.
Have you tried moving the valve manually, when the boiler is running? It might break the connection to the boiler

[TooLateForAName]

zone valve.

The room or tank thermostat controls the opening of the zone valve and a microswitch inside the zone valve controls the boiler firing.

Zone valve sticks and boiler will run until the boiler thermostat causes cut off.

[Tiggsy]

lol...not sure what it would look like!

so if the valve is stuck open....and the tank is SUPER hot....the boiler will keep flicking off and on to keep it that way while the valve stays open 24/7? Hence a hot tank that never gets less than HOT and a boiler that fires up all hours of the day for a few mins at a time?

that sounds like me.

whats the cost of a plumber to swap a new valve in?

[TooLateForAName]

anonymous said:

[redacted]

This is not correct. swap the zone valve and stat around.

[essayer]

Tiggsy said:

lol...not sure what it would look like!

so if the valve is stuck open....and the tank is SUPER hot....the boiler will keep flicking off and on to keep it that way while the valve stays open 24/7? Hence a hot tank that never gets less than HOT and a boiler that fires up all hours of the day for a few mins at a time?

that sounds like me.

whats the cost of a plumber to swap a new valve in?

Sounds like you! No idea on rates but it is a very common situation, some valves can be swapped without letting water out, others need it drained, or might have gate valves either side, etc.

Google 'Honeywell zone valve' to see what it looks like

[NPI]

TooLateForAName said:

anonymous said:

[redacted]

This is not correct. swap the zone valve and stat around.

That's correct, but it might also easier to think of them on separate lines:

Time-Clock -> Cylinder 'Stat -> Zone Valve Motor -> Zone valve switch

Zone valve switch -> Boiler

So if the zone valve sticks open the boiler will run all the time, controlled only by its own thermostat. The cylinder will get as hot as the setting on the boiler 'stat, which might be 80C.

[Tiggsy]

NPI said:

That's correct, but it might also easier to think of them on separate lines:

Time-Clock -> Cylinder 'Stat -> Zone Valve Motor -> Zone valve switch

Zone valve switch -> Boiler

So if the zone valve sticks open the boiler will run all the time, controlled only by its own thermostat. The cylinder will get as hot as the setting on the boiler 'stat, which might be 80C.

ahhhh......is that why the tank stat is 60 but the tank is BOILING hot? All the time!!!!