Heating on, water cold: gas condensing boiler

[FiHH]

Often the hot water fails to come on in the mornings. It works better in winter for some reason, but doesn't always work then. It can usually but not always be made to work by increasing the central heating thermostat so that the boiler comes on. The boiler is a Vokera Eclipse 226 ESS condensing boiler, not a combi.
Two firms of plumbers/heating engineers have come out, checked everything and told me it must be working as there is no apparent fault. The thermostat on the hot water tank and the Drayton programmer have both been replaced but this made no difference. The light on the programmer comes on when it should.
Any ideas?

 

[JohnD]

Did the person you used replace parts after testing them and finding them faulty? Or was it a shot in the dark?

Did he say anything about the 3-port valve?

Post some pics of the pipes and other things around your boiler and hot-water cylinder please.

 

[FiHH]

Shot in the dark! Plumber suggested thermostat, controller was my idea. No mention of 3 port valve.

 

[Gasguru]

The irony...a condensing boiler fitted to an ancient cylinder

On this boiler you are likely to have a couple of 2 port motorised valves, follow the pipework from the boiler to the cylinder and post a pic.

 

[FiHH]

Here are the two valves under the boiler.
And can I ask, is the hot water tank really a problem for the boiler? I did get a quote for a replacement but was beyond my means at the time.

 

[JohnD]

may look like one of these

https://www.screwfix.com/search?search=port+valve

 

[Gasguru]

The issue is that when that boiler was fitted it would have been an expensive option...condensing boilers were not the norm back then and weren't compulsory.
Given the extra expense of a condensing boiler it would probably have made far more sense to fit a non condensing boiler and replaced the cylinder with one having shiny new foam lagging (to save heat loss).

 

[FiHH]

may look like one of these

https://www.screwfix.com/search?search=port+valve

I can't see anything that shape, just these cylindrical objects. Will go and have another look in case missed anything.

 

[FiHH]

Are these the valves?

 

[Deleted member 267285]

Where is the cylinder thermostat located, looks too far down to me. Also the valve(s) you’re looking for may be in the cylinder cupboard.

Edit: posted same time, yes those are the valves.

 

[FiHH]

Where is the cylinder thermostat located, looks too far down to me. Also the valve(s) you’re looking for may be in the cylinder cupboard.

Edit: posted same time, yes those are the valves.

Cylinder thermostat is about a sixth of the way up from the bottom, where the plumber installed it.

 

[Gasguru]

Yes the cylinder stat's about right.

Remove that insulation from around the silver actuators on the motorised valves...the motors need airflow so as not to overheat and shorten their life.

When the timeclock is in a programmed "on" time it feeds 240V to the cylinder thermostat. If the stat is "calling" for heat the contacts inside are closed and it feeds 240v to the motor inside the cylinder zone valve.
The now energised motor should fully open the valve and at some point during this opening a switch is closed telling the boiler to fire up.

You need to investigate whether this motor is opening fully...I suspect not.

The motor can normally be replaced if it is found to be weak or failing.

 

[ianmcd]

For your reference you have a fully pumped sealed system on S plan, and agree sounds like you have a faulty DHW 2 port zone valve

 

[FiHH]

Many thanks, looks like another visit from the plumber then.

 

[Gasguru]

Surely not the same parts swappers though..your system doesn't get much simpler.