Lack of hot water

[jtheobald]

I hope somebody can kindly point me in the right direction, please.

Our house has a combi that feeds the water to the bathrooms etc. on one side of the house. On the other side of the house we still have a HW water tank (fed by the combi) that supplies hot water to another bathroom. Whilst the direct hot water from the combi is hot, the water from the tank is at best, lukewarm.

For some reason there are two motorized valves (as picture) to the tank. I have put the second valve (lower) into manual. The top valve has no resistance, but I am under the impression that it's stuck in an open position so it shouldn't stop hot water flowing (?); when the HW water timer activates the valve does seem to do something but I can't put it into manual, due to the lack of resistance.

Could it possibly be the tank thermostat (to my knowledge is way over 10 years old)? I cannot understand how the water is lukewarm, and not stone cold.

At times the water to the valve does heat up, but not for long!

My assumptions could be way off, so please correct me if wrong.

Many thanks.

 

[Harry Bloomfield]

Could it possibly be the tank thermostat (to my knowledge is way over 10 years old)? I cannot understand how the water is lukewarm, and not stone cold.

If the water in the cylinder is not hot enough, then try adjusting the cylinder thermostat up and down - you should hear it click on, and off, at the temperature it believes the cylinder is. They are not very accurate, +/-10C, but it will give you an idea whether the stat has failed.

As the stat clicks, you should also hear the valve actuator move too.

Keep in mind, that to heat the water in the cylinder, the circulated water needs to be some 10C hotter - is the boiler running at a high enough temperature?

 

[jtheobald]

If the water in the cylinder is not hot enough, then try adjusting the cylinder thermostat up and down - you should hear it click on, and off, at the temperature it believes the cylinder is. They are not very accurate, +/-10C, but it will give you an idea whether the stat has failed.

As the stat clicks, you should also hear the valve actuator move too.

Keep in mind, that to heat the water in the cylinder, the circulated water needs to be some 10C hotter - is the boiler running at a high enough temperature?

Hi Harry, thanks for your answer.

The only sound I get from the thermostat is if I turn it fully down (40). As you rightly say I do hear the value activate as well. I don't hear any other clicks other than that.

The boiler is close to maximum,

The one thing I didn't mention, as I thought it was irrelevant was Bosch Worcester have done quite a lot of work on the boiler recently. However, as I said the rest of the hot water is working fine,.

 

[CountryFan]

I think you have 2 motorised valves as one will be heating and the other to control the heated water to the cylinder. Lack of resistance is usually an indicator that the valve is open, but if it’s not energising the microswitch then that’s likely why you have insufficient hot water. You could try it with the heating on and feel the pipes the other side of the valve going to the cylinder - this should tell you whether it’s a failed valve or just likely the actuator.

 

[jtheobald]

Thanks for reply. I did what you said and can only feel hot water for a short time.

I don't know if this is anything, but using the information Harry provided I looked at the temperature gauge on the boiler.
The temperature was 27c when set to 'e'. I turned it up to maximum and it's showing 59c. Does this seem right as I wouldn't expect to have it set at maximum all the time.

 

[CountryFan]

Thanks for reply. I did what you said and can only feel hot water for a short time.

I don't know if this is anything, but using the information Harry provided I looked at the temperature gauge on the boiler.
The temperature was 27c when set to 'e'. I turned it up to maximum and it's showing 59c. Does this seem right as I wouldn't expect to have it set at maximum all the time.

If it’s 27, then that’s far too low to heat a cylinder which is set for 60 degrees, so boiler temperature would need to be approx 65 to reach the 60, depending on runs and insulation.

 

[Harry Bloomfield]

The temperature was 27c when set to 'e'. I turned it up to maximum and it's showing 59c. Does this seem right as I wouldn't expect to have it set at maximum all the time.

Doing a fair bit of guessing here, as I'm no expert on boilers....

The 27C setting is maybe for your CH temperature, and that is the temperature of the water it is trying to heat your cylinder with. Setting it to 59C may prove to be the solution you need, but will be too hot for the CH in the warmer weather.

Note - to avoid Legionella, they usually recommend that the temperature of the stored water in the cylinder, be raised to 55 to 60C, at least once per week. Obviously, that means the water in the heating coil needs to be even higher, to achieve that, by perhaps 10C.

 

[jtheobald]

Thank you so much. I think I will be getting WB back again! (3rd times!)!

 

[jtheobald]

The CH is turned off for the summer.

I thought the temperature gauge was for HW, but it seems it's for CH. Therefore, I don't understand what controls the water temperature.

 

[CountryFan]

The CH is turned off for the summer.

I thought the temperature gauge was for HW, but it seems it's for CH. Therefore, I don't understand what controls the water temperature.

You’ll have 2 which are both operable - one for the hot water fed via the combi, the other being for heat for rads and cylinder. As we’ve mentioned the cylinder needs to be 60 to prevent legionella, so unfortunately, unless you can use the immersion over summer, then that radiator temperature setting will need to be 65, this shouldn’t bring your heating on as you’ve got a motorised valve for control.

 

[CountryFan]

Thank you so much. I think I will be getting WB back again! (3rd times!)!

What for?

 

[Harry Bloomfield]

The CH is turned off for the summer.

Your boiler needn't actually provide any heated water, into the radiators, in that case. So long as the boiler stat setting is high enough to heat the water in the cylinder itself.

Your boiler would only seem to have one manual flow temperature setting, which has to be shared between the CH and heating the cylinder. More modern systems, have independent flow temperature settings, for each, and can only do one at any one time.

 

[Harry Bloomfield]

What for?

Exactly! It seems your system is working exactly as designed to work, but has a bit of a limitation in use, which we have both tried to explain above. WB cannot help you.

 

[jtheobald]

You're both diamonds and I appreciate your help.... thank you.

 

[ericmark]

It seems an odd set-up, but motorised valve bleed levers feel slack if open. It seems many have a problem with domestic hot water (DHW) and one problem is loss of energy in the summer. In winter energy lost from pipework still heats the house, so not wasted, but in summer it could cause air conditioning to run, if luck enough to have it, or at least the house warmer than we want it.

I say this, as the last thing you want to do, is fix it, only to then rip it out again, since you have a tank thermostat it would seem it should open/close one of the valves. I would have expected turning the temperature up/down you would hear a valve opening and closing.

The normal way is some programmer feeds the thermostat, then the thermostat opens a motorised valve, then a micro switch in the valve triggers the boiler, the micro switches do fail.

I found my boiler would need to fire once a day for around 20 minutes to keep my tank hot. It was not a modulating boiler, so 20 kW for 20 minutes is around 7 kWh per day to keep the tank hot. On using an immersion heater, with an iboost+ so it actually says how much it uses, on average it shows 1.25 kWh per day. At standard electric cost this means about the same to heat with electric and in my case oil. Since I use off-peak or sun, it costs me a lot less to use electric.

This was when the boiler was fired once a day, if the boiler is fired more often, then losses from boiler and pipe work are even higher, the immersion it seems fires around once every 2.5 hours to maintain the cylinder temperature, if the boiler did the same, it would increase the loses.

For me having a cylinder of hot water is good, as I can use the sun and off-peak, but under sink mini hot water stores, would really reduce the time it takes to get hot water to the tap.

Last house I installed an instant gas DHW heater, mainly as I wanted the room the cylinder took up, but it did mean it took a long time for hot water to arrive at the taps, and one could not set the tap at a dribble, it had to be full on to get hot water, this was before the combi came out, but mother had a combi right next to the kitchen sink, and still if eco set on, near half a bowl of water before it got hot, and again could not set tap at a dribble. With eco off, it heated a small tank of water in the boiler, and was better for kitchen sink taps, but then the shower would go from cold to hot, then cold again, and finally hot and stay hot.

I had been told so many times that it was cheaper to heat DHW with gas, I belived it, what seems to be missed is energy lost every time the boiler and pipe work cools down.