hot radiators, lukewarm water

[grandad666]

Hi, I have a Baxi 552, I just moved into the house and I'm slowly starting to know it. I have heat in the radiators (pump starts when room thermostat clicks, as expected), but the hot water is barely lukewarm: not cold, but maybe 40C max. With the electric immersion heater I get proper hot water. The cylinder thermostat is a tiny thingy attached with an elastic strap which doesn't seem to have any dial to set a temperature, admittedly I should look closer at it, but not tonight. My questions at this point are:

1. how do I verify if the thermostat is working?
2. what else could be wrong?
3. in general: how to troubleshoot the problem?

Thanks in advance for your replies, and sorry, but I won't be able to check any answers until tomorrow night, busy day.

 

[Boilerman2]

Check the water level in the F&E tank in the loft you may have a stuck ball valve - it does sound like you would be wise to have a Gas Engineer give it all a good service and look over though

 

[grandad666]

Check the water level in the F&E tank in the loft you may have a stuck ball valve - it does sound like you would be wise to have a Gas Engineer give it all a good service and look over though

maybe I'm missing something, but wouldn't a stuck ball cause either overflowing of the tank (stuck on open) or NO hot water at all (stuck on close)? Doesn't the fact that I'm getting hot water with the immersion heater mean that water is flowing correctly into and out of the F&E tank?

 

[Boilerman2]

With the greatest respect and from your rambling question (confusing) Please humor me and check your F&E tank (it;s the small one) if the ball valve is stuck, AND if you have a Gravity hot water Primary circuit this may well be the reason your BOILER is not heating the water if this is not the case please reply with more facts including the type of controls and where fitted motorised valves etc etc

 

[grandad666]

With the greatest respect and from your rambling question (confusing) Please humor me and check your F&E tank (it;s the small one) if the ball valve is stuck, AND if you have a Gravity hot water Primary circuit this may well be the reason your BOILER is not heating the water if this is not the case please reply with more facts including the type of controls and where fitted motorised valves etc etc

Hi Boilerman, my questions are rambling and confusing because all I know about central heating I've learnt in the last 2 weeks from the internet (I'm sure you guessed)! Controls: I'm not sure if I recognize the components correctly, I hope this description is useful: the controls are ancient, a timer with 3 modes: auto, continuous, off and an on-off switch labeled "heating", a pump (red cylinder), a 3-way valve (green cylinder with 3 pipes, directly connected to the pump). From what I've read, could this be a fully pumped "Y-circuit"? However, I'm not sure whether the pump comes on when the water is directed to the hot water tank, and the boiler only stays on intermittently, even thought the water is still not hot.

By the way, I changed the cylinder thermostat, and it seems that the water is now warmer, but still not really hot after a couple of hours. How long should it take to have properly hot water? Could it be that the boiler thermostat is too low (currently on 2 - Baxi 552 remember).

Today is too late to check the F&E tank, I'll check it tomorrow. I'm still not sure why the water would be lukewarm with the boiler but hot with the immersion heater, can you explain why would this happen?

 

[tamz]

[Could it be that the boiler thermostat is too low (currently on 2 - Baxi 552 remember).

2 is around 140 deg F (well it was when it was new 20 odd years ago). That is the temperature of the water leaving the boiler so your hot water can never rise above this.
Turn it up to high and see how it goes.
Your system is probably as old as your boiler and the cylinder may be fitted with a conversion coil. Depending on cylinder size 1 - 2 hours would not be uncommon for a reheat time.
The system may possibly be sludged up which will not help with the heat transfer.
Think about a new system or at least getting it cleaned out.

 

[grandad666]

Check the water level in the F&E tank in the loft you may have a stuck ball valve - it does sound like you would be wise to have a Gas Engineer give it all a good service and look over though

ok, gone into the loft (first time since I bought the house, and god it needs some sorting out!), and the ball valve is A-OK in both tanks. Will now try to increase the boiler temperature setting and report on that.

About the service: the previous owner had that done before the sale and everything was fine, except how the guy missed the TWO faulty thermostats is beyond me, he must've just looked at the boiler's gas connections.

Your system is probably as old as your boiler and the cylinder may be fitted with a conversion coil. Depending on cylinder size 1 - 2 hours would not be uncommon for a reheat time.
The system may possibly be sludged up which will not help with the heat transfer.
Think about a new system or at least getting it cleaned out.

The hot water tank is 117lt, brand new, which leaves me even more astonished by all the problems I'm having...

 

[oph]

Check the water level in the F&E tank in the loft you may have a stuck ball valve - it does sound like you would be wise to have a Gas Engineer give it all a good service and look over though

ok, gone into the loft (first time since I bought the house, and god it needs some sorting out!), and the ball valve is A-OK in both tanks. Will now try to increase the boiler temperature setting and report on that.

About the service: the previous owner had that done before the sale and everything was fine, except how the guy missed the TWO faulty thermostats is beyond me, he must've just looked at the boiler's gas connections.

Your system is probably as old as your boiler and the cylinder may be fitted with a conversion coil. Depending on cylinder size 1 - 2 hours would not be uncommon for a reheat time.
The system may possibly be sludged up which will not help with the heat transfer.
Think about a new system or at least getting it cleaned out.

The hot water tank is 117lt, brand new, which leaves me even more astonished by all the problems I'm having...

To be fair, if he was there servicing the boiler than thats all he'd be expected to do

 

[grandad666]

To be fair, if he was there servicing the boiler than thats all he'd be expected to do

yep, I guess you're right, the previous owners had every interest in trying to keep the service as cheap as possible...

 

[oph]

To be fair, if he was there servicing the boiler than thats all he'd be expected to do

yep, I guess you're right, the previous owners had every interest in trying to keep the service as cheap as possible...

unfortunatly thats 99% of the general public at large

 

[grandad666]

just an update: raising the boiler temperature setting didn't help. But now I have a clearer idea of what is happening: the water gets hot IF the heating is also on. What I think is happening is that the cylinder thermostat is just switching the 3-way valve, but not starting the pump. If the pump is running because the room thermostat is asking for water, then water can get to the hot water tank so... I hope it is just a case of incorrect wiring, hopefully just caused by me connecting the new thermostat. The cylinder thermostat has 3 wires coming into it: red, black and an uninsulated earth (I assume). Assuming standard color coding, which one is the common: the red or the black? The new thermostat has 3 terminals: COM, NO and NC, my guess for connections is: common -> COM and other wire -> NC (closed circuit when temperature < T0). The old thermostat is no help, lacking any marking. I could easily be wrong, and maybe the wiring issue is more complicated...

 

[grandad666]

more info on the system: it's an SMC system (see here http://www.gasman.fsbusiness.co.uk/fully_pumped_systems.htm under "SMC Controller"). The wiring seems ok, the cylinder thermostat triggers the bolier but not the pump (so the boiler switches itself off after a few seconds). I haven't actually tested whether the pump gets powered, but at this point I'm inclined to asking a pro to look the system over.

 

[grandad666]

ok, I had an electrician check the wiring, and he said it's fine: the pump receives power, it just doesn't work. the plumber said it's an ancient model and impossible to find (it's an SMC system with separate pumps for heating and hot water), any chance he could be wrong, is it still possible to find a replacement pump?

 

[Agile]

The SMC pumps are about 30 years old and hardly ever fail. But they are less powerful than modern types.

They can be replaced by any modern current pumps!

So I dont see why you think there is any problem.

Tony

 

[grandad666]

The SMC pumps are about 30 years old and hardly ever fail. But they are less powerful than modern types.
They can be replaced by any modern current pumps! So I dont see why you think there is any problem.

Tony

that's the plumber talking! It's the hot water pump, the one with 3 pipes connected to it, and I haven't seen anything like that on screwfix.com (suggestions for other places where I could look are welcome).