When heating is on, hot water never heats up

[Sarrusophone]

Hi all,

We have an old-ish open vented system. It may date to when our house was built in the late 1990s. The boiler is an Ideal Classic although I can’t see a model number anywhere on it.

It generally works ok, except that if the heating and hot water are both on at once, the hot water never really heats up.

I don’t think there is a problem with the 3-way valve. If I put the heating and hot water on at once, all three pipes from the 3-way valve become very hot very quickly which suggests to me the water is being circulated properly from the boiler to both the hot water cylinder and the radiators. However, the pipe coming out of the bottom of the hot water cylinder (i.e. the water returning to the boiler rather than that going to the taps) is only moderately warm after 30 minutes or so. Again, after 30 minutes on both, the water to the taps is only lukewarm whilst it would be hot enough to run a bath after about 20 minutes of the HW alone.

I don’t notice any impact on the radiators if both are on at once.

I had a chat a heating engineer who suggested that the pump (a Grundfos Selectric) might not be powerful enough (perhaps through wear) to circulate enough water to heat both. That seems like one possibility. But before we get him in with a view to doing that, I was wondering if there were any more investigations I could make?

I have read somewhere that there is a valve that is supposed to regulate the priority of flow of water between the HW and CH systems. I was wondering if that was overly-restricting the flow to the HW? If so, where might it be and how much would anyone suggest I adjust it? There’s a valve on the return pipe from the bottom of the cylinder: might that be it?

Any other thoughts?

Thanks very much!

 

[Agile]

Almost certainly!

If it is a gate valve then open it 4 half turns anticlockwise and see what difference that makes. Try to be accurate with your half turns.

Write down ALL the changes you make so that you can back track if needed to.

 

[Sarrusophone]

Thanks very much: I’ll give it a try.

 

[Sarrusophone]

Four half-turns has taken it exactly to the fully open position and, having put both the CH & HW on, the return pipe has immediately become much hotter than it was before. I’ll give it half-an-hour and see what the water temperature is like.

If that works, would you just leave it full open?

 

[Sarrusophone]

That seems to have done the trick. Thanks very much. I guess I just need to keep an eye on it and check that there are no resulting problems.

 

[Agile]

You have increased the proportional flow to the cylinder at the expense of the heating.

But it is unlikely you will notice any difference to the heating.

In any case heating has a long time constant and by the time there was any significant change to the heating the water will be hot and reheating it will turn off.


Others note his heating engineer was all for replacing the pump at a cost of perhaps £200 !

I like to start with simple no cost solutions!

 

[Harry Bloomfield]

Others note his heating engineer was all for replacing the pump at a cost of perhaps £200 !

I like to start with simple no cost solutions!

Well done that man!

I had in mind that the 3-port was perhaps giving priority to the CH, at the expense of the HW.

 

[ianmcd]

If you find that the rads get affected just keep balancing with that valve, until you get a happy medium

 

[Sarrusophone]

Thanks: will do.

Incidentally, I have no doubt that the chap I spoke to would have sorted this out for whatever his call-out fee was had we got him round to have a look rather than jumping straight in to replace the pump. At the time I spoke to him there was another problem which he correctly diagnosed over the phone and which I managed to fix. He also taught me enough about the system that I could trace this fault. Previously, I only had a really vague idea of how it worked and would have had no clue.

The suggestion of the pump replacement was very much in terms of “if something has broken it is most likely to be this but I’ll come around and have a look”. I was worried the boiler was packing up!

 

[ianmcd]

Thanks: will do.

Incidentally, I have no doubt that the chap I spoke to would have sorted this out for whatever his call-out fee was had we got him round to have a look rather than jumping straight in to replace the pump. At the time I spoke to him there was another problem which he correctly diagnosed over the phone and which I managed to fix. He also taught me enough about the system that I could trace this fault. Previously, I only had a really vague idea of how it worked and would have had no clue.

The suggestion of the pump replacement was very much in terms of “if something has broken it is most likely to be this but I’ll come around and have a look”. I was worried the boiler was packing up!

wasnt me that mentioned anything about the pump ?