Hot water coming on at random, thermostat not working?

[Andehh]

Long story short, our house is 7 years old, we moved in a few months ago. As per old house, we wanted a wireless programmable thermostat instead of one stuck on the wall.

It works fine in the sense hot water turns on/off as desired, heating comes on/off as desired.

Last few days though, we have had an issue where the boiler would fire on (thermostat saying it is off), a rad in the bathroom would get very hot (all others cold) and the hot water tank sounding like it is on/heating up. All this whilst the thermostat said the system was off.

After much head scratching I rang a plumber who very very kindly listened to my issue, was perplexed and said his guess was that the wireless thermostat was 'leaking' power through, meaning that it would turn the hot water off as switched, but was allowing enough power to leak through to allow the hot water to come on again when the temp dropped.

Now, this sounds very feasible. Hot water comes on for 30 mins early evening, we have showers then late evening it starts 'randomly' coming on for 5-10 mins at a time. He also guessed the rad getting hot in the bathroom is due to the system being set up so hot water on = someone wants a shower = rad in bathroom alone gets hot = warm shower, then warm room. Again, sounds feasible.


Now, I need to find a way to fix this. Would something as simple as a resistor (or such?) on the hot water switching side to reduce the voltage/thereby reducing the 'leakage' be enough to fix it? My friendly sparky fitted it a few weeks ago, so all work will be done by a professional, but I would like to ring him with some suggestions first.

Any suggestions? Cheers guys


edit: Thermostat:
http://www.heatmisershop.co.uk/ther...ss-programmable-thermostat-with-hw-output-p84

 

[EFLImpudence]

You're plumber's not an electrician, is he?

 

[Andehh]

Nope, sparky fitted the thermostat and he is an honest guy who I always use but has very limited knowledge, plumber I rang was making educated guesses. I'm an automotive engineer by trade, so between the three of us all we can confirm Is somethings not quite right!

 

[ianmcd]

cant wait to hear what Tony makes of this one, think you will need to fit something else that no one else has ever heard of !!!!!!!!

 

[EFLImpudence]

Last few days though, we have had an issue where the boiler would fire on (thermostat saying it is off), a rad in the bathroom would get very hot (all others cold) and the hot water tank sounding like it is on/heating up. All this whilst the thermostat said the system was off.

To be fair -

I do have a customer who's bathroom radiator is on the hot water pipe.
I don't know why but it is just plumbed that way - mistake ?


OP - When the boiler fires for the few minutes, does the light on the receiver show it is being signalled to turn on the water or does the system just start up due to a fault - sticky valve, perhaps?

 

[Andehh]

I'm totally stuck, after an evening of trying to get to the bottom of it, I'm clueless. Boiler fires at random, seems to heat hot water up despite thermostat showing it as off. If Rad in bathroom is on, it gets scorching hot - all other rads are cold.

Thermostat on/off makes no difference to boiler(hot water) firing. When boiler does turn off ( through my intervention or not) a maroon grundfos pump in the hot water tank cupboard keeps going. Turning the boiler off at the wall stops boiler and pump and they seem to stay off until boiler randomly re-engages, I still can't definitely say what the trigger is.

The only trigger *i think* is the hot water, radiators all (except bathroom) stay cold unless central heating is triggered by us, hot water is triggered correctly by thermostat as well. Just something is glitching in causing the hot water to get heated up when not asked for by thermostat.

Edit: when boiler fires by "mistake", thermostat nor LEDs on the front of the control box under boiler trigger. When it it comes on due to OUR timing/request it does & works perfectly.

Edit2: the plumber I spoke to did say that the bathroom Rad coming on with hot water is not uncommon, it's there so it warms the room out for when you step out the shower and helps dry towels etc when you have finished in the room.

 

[EFLImpudence]

If the led does not show then it likely is not the thermostat/receiver causing it.
Although I suppose some fault may do it.

Valve could be causing it but then the tank stat must still be calling for heat.

What temperature is the tank stat set to?

Pumps do run on for a while after boiler to cool it.

 

[Andehh]

Thermostat works absolutely fine, as timed for both hot water and central heating. One on a timerone set for different temps throughout the day to maintain. Other are mainly focused on early mornkng/when we get back from work whilst this issue tends to be mid-late evening.

Pump running due to heat sounds feasible, as I said if bathroom Rad is trv-on it gets scorching hot, of turned off... Heat is going somewhere?

How caniI tell the temp of tank? I only see a pressure valve. It is a megsflow/modern build setup.

Pics below: it is the left handpipes/pump that get very hot during this.

https://db.tt/xgu7JtbT
https://db.tt/omu4Xqm7

 

[EFLImpudence]

Ah, not what I had in mind and I'm not familiar with those but the principle is the same, I suppose.

Have a look at page 23 but you should get someone who is qualified with these systems to have a look.

 

[Agile]

Unfortunately I think that you are not correctly describing the various parts of your system.

So at the moment I cannot come to any conclusion about what you have got there.

Telling us make and model of wireless device would help. These are usually only for the heating but there are a few which will time a hot water channel as well and have a wireless sensor on the cylinder.

My conclusion so far I that its wrongly fitted or incompatible with your system.

I always recommend a heating engineer familiar with electronic controls to install them.

Tony

 

[EFLImpudence]

In OP

http://www.heatmisershop.co.uk/ther...ss-programmable-thermostat-with-hw-output-p84

It is two channel.

 

[Andehh]

Apologies, I should have listed them at the beginning.

The boiler is a Potterton promax HE plus, but with the standard wall mounted thermostat & programmer replaced with a wireless Heatmiser PRT/HW-WTS. The electrian who wired it in said it was a new model to him, but was a direct swap. It does work well with the hot water and heating working fine, except for this random boiler/hot water turning on.

The hot water cylinder is a megaflow Heatrae stadia. Nothing was touched In there.

Will speak to Heatmiser on Monday, my fear is not knowing if it is an electrical or plumbing issue, and associated bills from each as they both have a poke around

 

[Agile]

Thanks for pointing that out.

It is a wireless room stat with an additional timed channel for hot water!

But the cylinder will have a wired thermostat.

The complaints seems to be that the boiler will come on and heat the cylinder when the timing says that it is off.

There is no comment on whether the cylinder stat then controls the boiler.

There is no coment on whether the hot water motor valve is open or closed during this phantom "on" period.

To sus out the cause a lot of diagnostic information is needed. All of this will be redundant apart from the ONE aspect which will identify the cause of the problem.

Tony

 

[Andehh]

Thanks for pointing that out.

It is a wireless room stat with an additional timed channel for hot water!

But the cylinder will have a wired thermostat.

The complaints seems to be that the boiler will come on and heat the cylinder when the timing says that it is off.

There is no comment on whether the cylinder stat then controls the boiler.

There is no coment on whether the hot water motor valve is open or closed during this phantom "on" period.

To sus out the cause a lot of diagnostic information is needed. All of this will be redundant apart from the ONE aspect which will identify the cause of the problem.

Tony

Yes it is.

The wired thermostat, will be there to monitor the internal temp of the water? If we have the 'timed water' on for 4 hours, and it hits 'max temp' in 2 hours, then it shuts itself off unless temp drops?

yes, I believe this is the case.

I don't think the cylinder stat controls the boiler, I *think* the thermostat is just a 'hot water for 4 hours' control and then the boiler turns itself on/off during that period to achieve max temp. After 4 hours, thermostat lets hot water cool down till next '4 hour' cycle.

Where can I check the hot water Motor Valve? Research has led me to believe it is the Honeywell silver box at the very front of the cupboard, shown in the pics above^. It just has a lever on top of it.

I am very grateful for your suggestions & help, thank you!

 

[Agile]

Sorry, when writing that I missed your more detailed posting a minute before.

The cylinder stat should be wired so that it shuts the motor valve and shuts down the boiler.

This is probably where the problem lies.

But it creates a bit if a problem! Installing and repairing an unvented cylinder should only be done by someone qualified on them.

You seem to be separating electrical and plumbing aspects. The reality is that to correctly install these parts it needs someone with the unvented cert AND sufficient electrical knowledge. Not all have this.

But as far as I can tell your cylinder may well be dangerous because it lacks the correct wiring.

The cylinder has TWO stats. One for the regular control of stored water temperature by controlling the boiler.

The second is specifically a safety overheat stat with manual reset and this interrupts the supply to the motor valve to ensure it closes and shuts off the supply of further heat to the cylinder when it operates.

The only advice I can give here is to get a competent heating engineer familiar with and qualified to work on unventeds!

Tony